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vsearch(1)

USER COMMANDS

vsearch(1)

NAME
vsearch — chimera detection, clustering, dereplication and rereplication, FASTA/FASTQ file processing,
masking, pairwise alignment, searching, shuffling, sorting, subsampling, and taxonomic classification of
amplicons for metagenomics, genomics, and population genetics.

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Taxonomic classification:
vsearch --sintax fastafile --db fastafile --tabbedout outputfile [--sintax_cutoff real] [options]
UDB database handling:
vsearch --makeudb_usearch fastafile --output outputfile [options]
vsearch --udb2fasta udbfile --output outputfile [options]
vsearch (--udbinfo | --udbstats) udbfile [options]

DESCRIPTION
Environmental or clinical molecular diversity studies generate large volumes of amplicons (e.g.; SSUrRNA sequences) that need to be checked for chimeras, dereplicated, masked, sorted, searched, clustered or
compared to reference sequences. The aim of vsearch is to offer a all-in-one open source tool to perform
these tasks, using optimized algorithm implementations and harvesting the full potential of modern computers, thus providing fast and accurate data processing.
Comparing nucleotide sequences is at the core of vsearch. To speed up comparisons, vsearch implements
an extremely fast Needleman-Wunsch algorithm, making use of the Streaming SIMD Extensions (SSE2) of
post-2003 x86-64 CPUs. If SSE2 instructions are not available, vsearch exits with an error message. On
Power8 CPUs it will use AltiVec/VSX/VMX instructions. Memory usage increases rapidly with sequence
length: for example comparing two sequences of length 1 kb requires 8 MB of memory per thread, and
comparing two 10 kb sequences requires 800 MB of memory per thread. For comparisons involving
sequences with a length product greater than 25 million (for example two sequences of length 5 kb),
vsearch uses a slower alignment method described by Hirschberg (1975) and Myers and Miller (1988),
with much smaller memory requirements.
Input
vsearch accept as input fasta or fastq files containing one or several nucleotidic entries. In fasta files, each
nucleotidic entry is made of a header and a sequence. The header is defined as the string comprised
between the ’>’ symbol and the first space, tab or the end of the line, whichever comes first. Additionally, if
the header matches integer as the number of occurrences (or abundance) of the sequence in the study. That
abundance information is used or created during chimera detection, clustering, dereplication, sorting and
searching.
The sequence is defined as a string of IUPAC symbols (ACGTURYSWKMDBHVN), starting after the end
of the identifier line and ending before the next identifier line, or the file end. vsearch silently ignores ascii
characters 9 to 13, and exits with an error message if ascii characters 0 to 8, 14 to 31, ’.’ or ’-’ are present.
All other ascii or non-ascii characters are stripped and complained about in a warning message.
In fastq files, each entry is made of sequence header starting with a symbol ’@’, a nucleotidic sequence
(same rules as for fasta sequences), a quality header starting with a symbol ’+’ and a string of ASCII characters (offset 33 or 64), each one encoding the quality value of the corresponding position in the nucleotidic
sequence.
vsearch operations are case insensitive, except when soft masking is activated. Masking is automatically
applied during chimera detection, clustering, masking, pairwise alignment and searching. Soft masking is
specified with the options ’--dbmask soft’ (for searching and chimera detection with a reference) or
’--qmask soft’ (for searching, de novo chimera detection, clustering and masking). When using soft masking, lower case letters indicate masked symbols, while upper case letters indicate regular symbols. Masked
symbols are never included in the unique index words used for sequence comparisons, otherwise they are
treated as normal symbols.
When comparing sequences during chimera detection, dereplication, searching and clustering, T and U are
considered identical, regardless of their case. If two symbols are not identical, their alignment result in a
negative mismatch score (default -4), except if one or both of the symbols are ambiguous (RYSWKMDBHVN) in which case the score is zero. Alignment of two identical ambiguous symbols (for example, R vs
R) also receives a score of zero.
vsearch can read data from standard files and write to standard files, but it can also read from pipes and
write to pipes! For example, multiple fasta files can be piped into vsearch for dereplication. To do so, file

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names can be replaced with:
- the symbol ’-’, representing ’/dev/stdin’ for input files or ’/dev/stdout’ for output files,
- a named pipe created with the command mkfifo,
- a process substitution ’<(command)’ as input or ’>(command)’ as output.
vsearch can automatically read compressed gzip or bzip2 files if the appropriate libraries are present during
the compilation. vsearch can also read pipes streaming compressed gzip or bzip2 data if the options
--gzip_decompress or --bzip2_decompress are selected. When reading from a pipe, the progress indicator is
not updated.
Options
vsearch recognizes a large number of command-line options. For easier navigation, options are grouped
below by theme (chimera detection, clustering, dereplication and rereplication, FASTA/FASTQ file processing, masking, pairwise alignment, searching, shuffling, sorting, and subsampling). We start with the
general options that apply to all themes. Options may start with a single (-) or double dash (--). Option
names may be shortened as long as they are not ambiguous (e.g. --derep_f).
General options:
--bzip2_decompress
When reading from a pipe streaming bzip2-compressed data, decompress the data. That
option is not needed when reading from a standard bzip2-compressed file.
--fasta_width positive integer
Fasta files produced by vsearch are wrapped (sequences are written on lines of integer
nucleotides, 80 by default). Set that value to zero to eliminate the wrapping.
--gzip_decompress
When reading from a pipe streaming gzip-compressed data, decompress the data. That
option is not needed when reading from a standard gzip-compressed file.
--help | -h
Display help text and exit.
--log filename
Write messages to the specified log file. Information written includes program version,
amount of memory available, number of cores and command line options, and if need
be, informational messages, warnings and fatal errors. The start and finish times are
also recorded as well as the elapsed time and the maximum amount of memory consumed. The different vsearch commands can also write additional informations to
the log file.
--maxseqlength positive integer
All vsearch operations discard sequences of length equal or greater than integer
(50,000 nucleotides by default).
--minseqlength positive integer
All vsearch operations discard sequences of length smaller than integer: 1 nucleotide
by default for sorting or shuffling, 32 nucleotides for clustering, dereplication or
searching.
--no_progress
Do not show the gradually increasing progress indicator.
--notrunclabels
Do not truncate sequence labels at first space or tab, use the full header in output files.
--quiet

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--threads positive integer
Number of computation threads to use (1 to 256). The number of threads should be
lesser or equal to the number of available CPU cores. The default is to use all available
resources and to launch one thread per logical core. The following commands are
multi-threaded: allpairs_global, cluster_fast, cluster_size, cluster_smallmem,
fastq_mergepairs, maskfasta, search_exact, uchime_ref, and usearch_global. Only one
thread is used for the other commands.
--version | -v
Output version information and exit.
Chimera detection options:
Chimera detection is based on a scoring function controlled by five options (--dn, --mindiffs,
--mindiv, --minh, --xn). Sequences are first sorted by decreasing abundance, if available, and compared on their plus strand only (case insensitive).
Input sequences are masked as specified with the --qmask and --hardmask options. Masking of the
database for reference based chimera detection is specified with the --dbmask option.
In de novo mode, input fasta file should present abundance annotations (i.e. a pattern [;]size=integer[;] in the fasta header). Input order matters for chimera detection, so we recommend to sort
sequences by decreasing abundance (default of --derep_fulllength command). If your sequence set
needs to be sorted, please see the --sortbysize command in the sorting section.
--abskew real
When using --uchime_denovo, the abundance skew is used to distinguish in a threeway alignment which sequence is the chimera and which are the parents. The assumption is that chimeras appear later in the PCR amplification process and are therefore
less abundant than their parents. For --uchime3_denovo the default value is 16.0. For
the other commands, the default value is 2.0, which means that the parents should be at
least 2 times more abundant than their chimera. Any positive value equal or greater
than 1.0 can be used.
--alignwidth positive integer
When using --uchimealns, set the width of the three-way alignments (80 nucleotides by
default). Set to zero to eliminate wrapping.
--borderline filename
Output borderline chimeric sequences to filename, in fasta format. Borderline chimeric
sequences are sequences that have a high enough score but which are not sufficiently
different from their closest parent.
--chimeras filename
Output chimeric sequences to filename, in fasta format. Output order may vary when
using multiple threads.
--db filename
When using --uchime_ref, detect chimeras using the fasta-formatted reference
sequences contained in filename. Reference sequences are assumed to be chimera-free.
Chimeras cannot be detected if their parents, or sufficiently close relatives, are not
present in the database.
--dn real No vote pseudo-count, corresponding to the parameter n in the chimera scoring function (default value is 1.4).
--fasta_score
Add the chimera score to the headers in the fasta output files for chimeras, nonchimeras and borderline sequences, using the format

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--mindiffs positive integer
Minimum number of differences per segment (default value is 3). The parameter is
ignored with --uchime2_denovo and --uchime3_denovo.
--mindiv real
Minimum divergence from closest parent (default value is 0.8). The parameter is
ignored with --uchime2_denovo and --uchime3_denovo.
--minh real
Minimum score (h). Increasing this value tends to reduce the number of false positives
and to decrease sensitivity. Default value is 0.28, and values ranging from 0.0 to 1.0
included are accepted. The parameter is ignored with --uchime2_denovo and
--uchime3_denovo.
--nonchimeras filename
Output non-chimeric sequences to filename, in fasta format. Output order may vary
when using multiple threads.
--relabel string
Relabel sequences using the prefix string and a ticker (1, 2, 3, etc.) to construct the new
headers. Use --sizeout to conserve the abundance annotations.
--relabel_keep
When relabelling, keep the old identifier in the header after a space.
--relabel_md5
Relabel sequences using the MD5 message digest algorithm applied to each sequence.
Former sequence headers are discarded. The sequence is converted to upper case and
each ’U’ is replaced by a ’T’ before computation of the digest. The MD5 digest is a
cryptographic hash function designed to minimize the probability that two different
inputs give the same output, even for very similar, but non-identical inputs. Still, there
is a very small, but non-zero, probability that two different inputs give the same digest
(i.e. a collision). MD5 generates a 128-bit (16-byte) digest that is represented by 16
hexadecimal numbers (using 32 symbols among 0123456789abcdef). Use --sizeout to
conserve the abundance annotations.
--relabel_sha1
Relabel sequences using the SHA1 message digest algorithm applied to each sequence.
It is similar to the --relabel_md5 option but uses the SHA1 algorithm instead of the
MD5 algorithm. SHA1 generates a 160-bit (20-byte) digest that is represented by 20
hexadecimal numbers (40 symbols). The probability of a collision (two non-identical
sequences resulting in the same digest) is smaller for the SHA1 algorithm than it is for
the MD5 algorithm.
--self

When using --uchime_ref, ignore a reference sequence when its label matches the label
of the query sequence (useful to estimate false-positive rate in reference sequences).

--selfid

When using --uchime_ref, ignore a reference sequence when its nucleotide sequence is
strictly identical to the nucleotidic sequence of the query.

--sizeout When relabelling, add abundance annotations to fasta headers (using the format
’;size=integer;’).
--uchime_denovo filename
Detect chimeras present in the fasta-formatted filename, without external references
(i.e. de novo). Automatically sort the sequences in filename by decreasing abundance
beforehand (see the sorting section for details). Multithreading is not supported.
--uchime2_denovo filename
Detect chimeras present in the fasta-formatted filename, using the UCHIME2 algorithm. This algorithm is designed for denoised amplicons (see --cluster_unoise). Automatically sort the sequences in filename by decreasing abundance beforehand (see the

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sorting section for details). Multithreading is not supported.
--uchime3_denovo filename
Detect chimeras present in the fasta-formatted filename, using the UCHIME2 algorithm. The only difference from --uchime2_denovo is that the default minimum abundance skew (--abskew) is set to 16.0 rather than 2.0.
--uchime_ref filename
Detect chimeras present in the fasta-formatted filename by comparing them with reference sequences (option --db). Multithreading is supported.
--uchimealns filename
Write the three-way global alignments (parentA, parentB, chimera) to filename using a
human-readable format. Use --alignwidth to modify alignment length. Output order
may vary when using multiple threads. All sequences are converted to upper case
before alignment. Lower case letters indicate disagreement in the alignment.
--uchimeout filename
Write chimera detection results to filename using a 18-field, tab-separated uchime-like
format. Use --uchimeout5 to use a format compatible with usearch v5 and earlier versions. Rows output order may vary when using multiple threads.
1.

score: higher score means a more likely chimeric alignment.

Q: query sequence label.

A: parent A sequence label.

B: parent B sequence label.

T: top parent sequence label (i.e. parent most similar to the query). That
field is removed when using --uchimeout5.

idQM: percentage of similarity of query (Q) and model (M) constructed
as a part of parent A and a part of parent B.

idQA: percentage of similarity of query (Q) and parent A.

idQB: percentage of similarity of query (Q) and parent B.

idAB: percentage of similarity of parent A and parent B.

10. idQT: percentage of similarity of query (Q) and top parent (T).
11. LY: yes votes in the left part of the model.
12. LN: no votes in the left part of the model.
13. LA: abstain votes in the left part of the model.
14. RY: yes votes in the right part of the model.
15. RN: no votes in the right part of the model.
16. RA: abstain votes in the right part of the model.
17. div: divergence, defined as (idQM - idQT).
18. YN: query is chimeric (Y), or not (N), or is a borderline case (?).
--uchimeout5
When using --uchimeout, write chimera detection results using a 17-field, tab-separated
uchime-like format (drop the 5th field of --uchimeout), compatible with usearch version 5 and earlier versions.
--xn real No vote weight, corresponding to the parameter beta in the scoring function (default
value is 8.0).

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--xsize

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Strip abundance information from the headers when writing the output file.

Clustering options:
vsearch implements a single-pass, greedy centroid-based clustering algorithm, similar to the algorithms implemented in usearch, DNAclust and sumaclust for example. Important parameters are
the global clustering threshold (--id) and the pairwise identity definition (--iddef).
Input sequences are masked as specified with the --qmask and --hardmask options.
--biomout filename
Generate an OTU table in the biom version 1.0 JSON file format as specified at
http://biom-format.org/documentation/format_versions/biom-1.0.html. The format
describes how to store a sparse matrix containing the abundances of the OTUs in the
different samples. This format is much more efficient than the classic and mothur OTU
table formats available with the --otutabout and --mothur_shared_out options, respectively, and is recommended at least for large tables. The OTUs are represented by the
cluster centroids. Taxonomy information will be included for the OTUs if available.
Sample identifiers will be extracted from the headers of all sequences in the input file.
If the header contains ’;sample=abc123;’ or ’;barcodelabel=abc123;’ or a similar string
somewhere, then the given sample identifier (here ’abc123’) will be used. The semicolon is not mandatory at the beginning or end of the header. The sample identifier may
contain any printable character except semicolons. If no such sample label is found, the
identifier in the initial part of the header will be used, but only letters, digits and underscores are allowed. OTU identifiers will be extracted from the headers of the cluster
centroid sequences. If the header contains ’;otu=def789;’ or a similar string somewhere, then the given OTU identifier (here ’def789’) will be used. The semicolon is not
mandatory at the beginning or end of the header. The OTU identifier may contain any
printable character except semicolons. If no such OTU label is found, the identifier in
the initial part of the header will be used, and all characters except semicolons are
allowed. Alternatively, OTU identifers can be generated using the relabelling options
(--relabel, --relabel_sha1 or --relabel_md5). Taxonomy information, if present, will
also be extracted from the headers of the centroid sequences. If the header contains
’;tax=Homo_sapiens;’ or a similar string somewhere, then the given taxonomy information (here ’Homo_sapiens’) will be used. The semicolon is not mandatory at the
beginning or end of the header. The taxonomy information may contain any printable
character except semicolons. If an OTU table in the biom version 2.1 HDF5 file format
is required, the biom utility may be used as described at http://biom-format.org/documentation/biom_conversion.html.
--centroids filename
Output cluster centroid sequences to filename, in fasta format. The centroid is the
sequence that seeded the cluster (i.e. the first sequence of the cluster).
--clusterout_id
Add cluster identifier information to the output files when using the --consout and
--profile options.
--clusterout_sort
Sort output files by decreasing abundance when using the --consout, --msaout and
--profile options.
--cluster_fast filename
Clusterize the fasta sequences in filename, automatically sort by decreasing sequence
length beforehand.
--cluster_size filename
Clusterize the fasta sequences in filename, automatically sort by decreasing sequence
abundance beforehand.

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--cluster_smallmem filename
Clusterize the fasta sequences in filename without automatically modifying their order
beforehand. Sequence are expected to be sorted by decreasing sequence length, unless
--usersort is used.
--cluster_unoise filename
Perform denoising of the fasta sequences in filename according to the UNOISE version
3 algorithm by Robert Edgar, but without the chimera removal step. The options --minsize (default 8) and --unoise_alpha (default 2.0) may be specified. Chimera removal (de
novo) should be performed afterwards with --uchime3_denovo.
--clusters string
Output each cluster to a separate fasta file using the prefix string and a ticker (0, 1, 2,
etc.) to construct the path and filenames.
--consout filename
Output cluster consensus sequences to filename. For each cluster, a multiple alignment
is computed, and a consensus sequence is constructed by taking the majority symbol
(nucleotide or gap) from each column of the alignment. Columns containing a majority
of gaps are skipped, except for terminal gaps.
--cons_truncate
This command is ignored. A warning is issued.
--id real Do not add the target to the cluster if the pairwise identity with the centroid is lower
than real (value ranging from 0.0 to 1.0 included). The pairwise identity is defined as
the number of (matching columns) / (alignment length - terminal gaps). That definition
can be modified by --iddef.
--iddef 0|1|2|3|4
Change the pairwise identity definition used in --id. Values accepted are:
0.

CD-HIT definition: (matching columns) / (shortest sequence length).

edit distance: (matching columns) / (alignment length).

edit distance excluding terminal gaps (same as --id).

Marine Biological Lab definition counting each gap opening (internal or
terminal) as a single mismatch, whether or not the gap was extended: 1.0
- [(mismatches + gap openings)/(longest sequence length)]

BLAST definition, equivalent to --iddef 1 in a context of global pairwise
alignment.

--minsize positive integer
Specify the minimum abundance of sequences for denoising using --cluster_unoise.
The default is 8.
--msaout filename
Output a multiple sequence alignment and a consensus sequence for each cluster to filename, in fasta format. Be warned that vsearch computes center star multiple sequence
alignments using a fast method whose accuracy can decrease significantly when using
low pairwise identity thresholds. The consensus sequence is constructed by taking the
majority symbol (nucleotide or gap) from each column of the alignment. Columns containing a majority of gaps are skipped, except for terminal gaps.
--mothur_shared_out filename
Output an OTU table in the mothur ’shared’ tab-separated plain text format as
described at http://www.mothur.org/wiki/Shared_file. The format describes how a
matrix containing the abundances of the OTUs in the different samples is stored. The
first line will start with the strings ’label’, ’group’ and ’numOtus’ and is followed by a
list of all OTU identifiers. The following lines, one for each sample, starts with the

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string ’vsearch’ followed by the sample identifier, the total number of OTUs, and a list
of abundances for each OTU in that sample, in the order given on the first line. The
OTU and sample identifiers are extracted from the FASTA headers of the sequences.
The OTUs are represented by the cluster centroids. See the --biomout option for further
details.
--otutabout filename
Output an OTU table in the classic tab-separated plain text format as a matrix containing the abundances of the OTUs in the different samples. The first line will start with
the string ’#OTU ID’ and is followed by a tab-separated list of all sample identifiers.
The following lines, one for each OTU, starts with the OTU identifier and is followed
by a tab-separated list of abundances for that OTU in each sample, in the order given
on the first line. The OTU and sample identifiers are extracted from the FASTA headers
of the sequences. The OTUs are represented by the cluster centroids. An extra column
is added to the right of the table if taxonomy information is available for at least one of
the OTUs. This column will be labelled ’taxonomy’ and each row will then contain the
taxonomy information extracted for that OTU. See the --biomout option for further
details.
--profile filename
Output a sequence profile to a text file with the frequency of each nucleotide in each
position in the multiple alignment for each cluster. There is a FASTA-like header line
for each cluster, followed by the profile information in a tab-separated format. The
eight columns are: position (0-based), consensus nucleotide, number of As, number of
Cs, number of Gs, number of Ts or Us, number of gap symbols, and finally the total
number of ambiguous nucleotide symbols (B, D, H, K, M, N, R, S, Y, V or W). All
numbers are integers.
--qmask none|dust|soft
Mask regions in sequences using the dust or the soft methods, or do not mask (none).
Warning, when using soft masking, clustering becomes case sensitive. The default is to
mask using dust.
--relabel string
Relabel sequence identifiers in the output files produced by --consout, --profile and
--centroids options. Please see the description of the same option under Chimera detection for details.
--relabel_keep
When relabelling, keep the old identifier in the header after a space.
--relabel_md5
Relabel sequence identifiers in the output files produced by --consout, --profile and
--centroids options. Please see the description of the same option under Chimera detection for details.
--relabel_sha1
Relabel sequence identifiers in the output files produced by --consout, --profile and
--centroids options. Please see the description of the same option under Chimera detection for details.
--sizein

Take into account the abundance annotations present in the input fasta file (search for
the pattern ’[>;]size=integer[;]’ in sequence headers).

--sizeorder
When an amplicon is close to 2 or more centroids, both within the distance specified
with the --id option, resolve the ambiguity by clustering it with the centroid having the
highest abundance, not necessarily the closest one. The option only has effect when the
value specified with --maxaccepts is higher than one. The --sizeorder option turns on
what is sometimes referred to as abundance-based greedy clustering (AGC), in contrast

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to the default distance-based greedy clustering (DGC).
--sizeout Add abundance annotations to the output fasta files (add the pattern specified, abundance annotations are reported to output files, and each cluster centroid receives a new
abundance value corresponding to the total abundance of the amplicons included in the
cluster (--centroids option). If --sizein is not specified, input abundances are set to 1 for
amplicons, and to the number of amplicons per cluster for centroids.
--strand plus|both
When comparing sequences with the cluster seed, check the plus strand only (default)
or check both strands.
--uc filename
Output clustering results in filename using a tab-separated uclust-like format with 10
columns and 3 different type of entries (S, H or C). Each fasta sequence in the input file
can be either a cluster centroid (S) or a hit (H) assigned to a cluster. Cluster records (C)
summarize information (size, centroid label) for each cluster. In the context of clustering, the option --uc_allhits has no effect on the --uc output. Column content varies with
the type of entry (S, H or C):
1.

Record type: S, H, or C.

Cluster number (zero-based).

Centroid length (S), query length (H), or cluster size (C).

Percentage of similarity with the centroid sequence (H), or set to ’*’ (S,
C).

Match orientation + or - (H), or set to ’*’ (S, C).

Not used, always set to ’*’ (S, C) or to zero (H).

set to ’*’ (S, C) or, for H, compact representation of the pairwise alignment using the CIGAR format (Compact Idiosyncratic Gapped Alignment Report): M (match), D (deletion) and I (insertion). The equal sign
’=’ indicates that the query is identical to the centroid sequence.

Label of the query sequence (H), or of the centroid sequence (S, C).

10. Label of the centroid sequence (H), or set to ’*’ (S, C).
--unoise_alpha real
Specify the alpha parameter to the --cluster_unoise command. The default i 2.0.
--usersort
When using --cluster_smallmem, allow any sequence input order, not just a decreasing
length ordering.
--xsize

Strip abundance information from the headers when writing the output file.

...

Most searching options as well as score filtering, gap penalties and masking also apply
to clustering (see the Searching section for definitions): --alnout, --blast6out,
--fastapairs, --matched, --notmatched, --maxaccept, --maxreject, --samout, --userout,
--userfields

Dereplication and rereplication options:
--derep_fulllength filename
Merge strictly identical sequences contained in filename. Identical sequences are
defined as having the same length and the same string of nucleotides (case insensitive,
T and U are considered the same). See the options --sizein and --sizeout to take into
account and compute abundance values.

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--derep_prefix filename
Merge sequences with identical prefixes contained in filename. A short sequence identical to an initial segment (prefix) of another sequence is considered a replicate of the
longer sequence. If a sequence is identical to the prefix of two or more longer
sequences, it is clustered with the shortest of them. If they are equally long, it is clustered with the most abundant. Remaining ties are solved using sequence headers and
sequence input order. Sequence comparisons are case insensitive, and T and U are considered identical.
--maxuniquesize positive integer
Discard sequences with a post-dereplication abundance value greater than integer.
--minuniquesize positive integer
Discard sequences with a post-dereplication abundance value smaller than integer.
--output filename
Write the dereplicated sequences to filename, in fasta format and sorted by decreasing
abundance. Identical sequences receive the header of the first sequence of their group.
If --sizeout is used, the number of occurrences (i.e. abundance) of each sequence is
indicated at the end of their fasta header using the pattern
--relabel string
Please see the description of the same option under Chimera detection for details.
--relabel_keep
When relabelling, keep the old identifier in the header after a space.
--relabel_md5
Please see the description of the same option under Chimera detection for details.
--relabel_sha1
Please see the description of the same option under Chimera detection for details.
--rereplicate filename
Duplicate each sequence the number of times indicated by the abundance of each
sequence in the specified file (option --sizein is always implied). The sequence labels
are identical for the same sequence, unless --relabel, --relabel_sha1 or --relabel_md5 is
used to create unique labels. Output is written to the file specified with the --output
option, in FASTA format. The output file does not contain abundance information
unless --sizeout is specified, in which case an abundance of 1 is used.
--sizein

Take into account the abundance annotations present in the input fasta file (search for
the pattern ’[>;]size=integer[;]’ in sequence headers). That option is active by default
when rereplicating.

--sizeout Add abundance annotations to the output fasta file (add the pattern specified, each
unique sequence receives a new abundance value corresponding to its total abundance
(sum of the abundances of its occurrences). If --sizein is not specified, input abundances are set to 1, and each unique sequence receives a new abundance value corresponding to its number of occurrences in the input file.
--strand plus|both
When searching for strictly identical sequences, check the plus strand only (default) or
check both strands.
--topn positive integer
Output only the top integer sequences (i.e. the most abundant).
--uc filename
Output full-length or prefix-dereplication results in filename using a tab-separated
uclust-like format with 10 columns and 3 different type of entries (S, H or C). Each
fasta sequence in the input file can be either a cluster centroid (S) or a hit (H) assigned

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to a cluster. Cluster records (C) summarize information (size, centroid label) for each
cluster. In the context of dereplication, the option --uc_allhits has no effect on the --uc
output. Column content varies with the type of entry (S, H or C):
1.

Record type: S, H, or C.

Cluster number (zero-based).

Sequence length (S, H), or cluster size (C).

Percentage of similarity with the centroid sequence (H), or set to ’*’ (S,
C).

Match orientation + or - (H), or set to ’*’ (S, C).

Not used, always set to ’*’ (S, C) or 0 (H).

Not used, always set to ’*’.

Label of the query sequence (H), or of the centroid sequence (S, C).

10. Label of the centroid sequence (H), or set to ’*’ (S, C).
--xsize

Strip abundance information from the headers when writing the output file.

FASTA/FASTQ file processing options:
Analyse, shorten, filter, convert or merge sequences in FASTQ files, or reverse complement
sequences in FASTA or FASTQ files. The --fastq_chars command can be used to analyse FASTQ
files to identify the quality encoding and the range of quality score values used. To convert
between different FASTQ file variants, use the --fastq_convert command. Statistical analysis of the
quality and length of the sequences in a FASTQ file may be performed with the --fastq_stats,
--fastq_eestats, and --fastq_eestats2 commands. Sequences may be shortened, filtered and converted by the --fastq_filter or --fastx_filter commands. Paired-end reads can be merged using the
--fastq_mergepairs command. The --fastx_revcomp command reverse-complements sequences.
Finally, the --sff_convert command can be used to convert SFF files to FASTQ.
--eeout

When using --fastq_filter or --fastq_mergepairs, include the number of expected errors
(ee) in the sequence header of FASTQ and FASTA files. This option is a synonym of
the --fastq_eeout option.

--eetabbedout filename
When specified with the --fastq_mergepairs command, write statistics with expected
errors of each merged read to the given file. The file is a tab separated file with four
columns: The number of errors expected in the forward read, the number of expected
errors in the reverse read, the number of observed errors in the forward read, and the
number of observed errors in the reverse read. The observed number of errors are the
number of differences in the overlap region of the merged sequence relative to each of
the reads in the pair.
--fastaout filename
When using --fastq_filter, --fastq_mergepairs or --fastx_filter, write to the given
FASTA-formatted file the sequences passing the filter, or the merged sequences.
--fastaout_notmerged_fwd filename
When using --fastq_mergepairs, write forward reads not merged to the specified
FASTA file.
--fastaout_notmerged_rev filename
When using --fastq_mergepairs, write reverse reads not merged to the specified FASTA
file.

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--fastaout_discarded filename
Write sequences that do not pass the filter of the --fastq_filter or --fastx_filter command
to the given FASTA-formatted file.
--fastq_allowmergestagger
When using --fastq_mergepairs, allow to merge staggered read pairs. Staggered pairs
are pairs where the 3’ end of the reverse read has an overhang to the left of the 5’ end
of the forward read. This situation can occur when a very short fragment is sequenced.
The 3’ overhang of the reverse read is not included in the merged sequence. The opposite option is the --fastq_nostagger option. The default is to discard staggered pairs.
--fastq_ascii positive integer
Define the ASCII character number used as the basis for the FASTQ quality score. The
default is 33, which is used by the Sanger / Illumina 1.8+ FASTQ format (phred+33).
The value 64 is used by the Solexa, Illumina 1.3+ and Illumina 1.5+ formats
(phred+64).
--fastq_asciiout positive integer
When using --fastq_convert or --sff_convert, define the ASCII character number used
as the basis for the FASTQ quality score when writing FASTQ output files. The default
is 33.
--fastq_chars filename
Summarize the composition of sequence and quality strings contained in the input
FASTQ file. For each of the four DNA letters, --fastq_chars gives the number of occurrences of the letter, its relative frequency and the length of the longest run of that letter.
For each character present in the quality strings, --fastq_chars gives the ASCII value of
the character, its relative frequency, and the number of times a k-mer of that character
appears at the end of quality strings. The length of the k-mer can be set using
--fastq_tail (4 by default). The command --fastq_chars tries to automatically detect the
quality encoding (Solexa, Illumina 1.3+, Illumina 1.5+ or Illumina 1.8+/Sanger) by
analyzing the range of observed quality score values. In case of success, --fastq_chars
suggests values for the --fastq_ascii (33 or 64), --fastq_qmin and --fastq_qmax options
to be used with the other commands that require a FASTQ input file.
--fastq_convert filename
Convert between the different variants of the FASTQ file format. The quality encoding
of the input file must be specified with the --fastq_ascii option (either 33 or 64, the
default is 33), and the output quality encoding must be specified with the --fastq_asciiout option (default 33). The minimum and maximum output quality scores may be
limited using the --fastq_qminout and --fastq_qmaxout options. The output file is specified with the --fastqout option.
--fastq_eeout
When using --fastq_filter or --fastq_mergepairs, include the number of expected errors
(ee) in the sequence header of FASTQ and FASTA files. This option is a synonym of
the --eeout option.
--fastq_eestats filename
Analyze a FASTQ file and report statistics on the distributions of quality scores, error
probabilities and expected accumulated errors. The report, a table of 21 tab-separated
columns, is written to the file specified with the --output option. The first column corresponds to the position in the reads (Pos). The second and third columns correspond to
the number of reads (Reads) and percentage of reads (PctRecs) that include this position. The remaining columns include information about the distribution of quality
scores in this position (Q), error probabilities in this position (Pe), and finally the
expected number of accumulated errors from the beginning of the reads and until the
current position (EE). For each of the Q, Pe and EE distributions, the following statistics are included: minimum value (Min), lower quartile (Low), median (Med), mean

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(Mean), upper quartile (Hi), and maximum value (Max). The quality encoding and the
range of quality values may be specified with --fastq_ascii --fastq_qmin and
--fastq_qmax.
--fastq_eestats2 filename
Analyze the specified FASTQ file and report statistics on the number of sequences that
would be retained at a combination of selected cutoffs for length truncation and maximum expected errors, that could potentially be used as arguments to the --fastq_trunclen and --fastq_maxee options to the --fastq_filter command. The result, a table of
two or more columns, is written to the file specified with the --output option. There is a
line for each length truncation cutoff. The first column on each line contains the
selected truncation length, while the following columns contain the number of
sequences and, in parenthesis, the percentage of sequences that would be retained at the
selected EE levels. The truncation length cutoffs may be specified with the
--length_cutoffs option and requires a list of three comma-separated integers indicating
the shortest cutoff, the longest cutoff, and the increment between cutoffs. The longest
cutoff may be specified with a star (*) which indicates that the limit is equal to the
longest sequence in the input file. The default setting is "50,*,50" meaning that truncation lengths of 50, 100, 150 and so on up to the longest sequence length should be
used. The maximum expected error (EE) cutoffs may be specified with the --ee_cutoffs
option which requires a comma-separated list of floating point numbers as its argument. The default setting is "0.5,1.0,2.0" that indicates that expected error levels of 0.5,
1.0 and 2.0 should be used.
--fastq_filter filename
Shorten and/or filter sequences in the given FASTQ file. Similar to the --fastx_filter
command, but works only on FASTQ files. See --fastx_filter for details.
--fastq_join filename
Join paired-end sequence reads into one sequence and add a gap between them using a
padding sequence. The sequences are not merged as with the fastq_mergepairs command, but simply joined with a gap. The forward reads are specified as the argument to
this option and the reverse reads are specified with the --reverse option. The resulting
sequences consist of the forward read, the padding sequence and the reverse complement of the reverse read. The padding sequence is specified with the --join_padgap
option and the padding quality is specified with the --join_padgapq option. The default
padding sequence string is NNNNNNNN and the default padding quality string is IIIIIIII, corresponding to a base quality score of 40 (a very high quality score with error
probability 0.0001). The joined sequences are output to the file(s) specified with the
--fastaout or --fastqout options.
--fastq_maxdiffs positive integer
When using --fastq_mergepairs, specify the maximum number of non-matching
nucleotides allowed in the overlap region. That option has a strong influence on the
merging success rate. The default value is 10.
--fastq_maxdiffpct real
When using --fastq_mergepairs, specify the maximum percentage of non-matching
nucleotides allowed in the overlap region. The default value is 100.0%. There are other
more sophisticated rules in the merging algorithm that will discard read pairs with a
high fraction of mismatches.
--fastq_maxee real
When using --fastq_filter, --fastq_mergepairs or --fastx_filter, discard sequences with
more than the specified number of expected errors.
--fastq_maxee_rate real
When using --fastq_filter or --fastx_filter, discard sequences with more than the specified number of expected errors per base.

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--fastq_maxlen positive integer
When using --fastq_filter, --fastq_mergepairs or --fastx_filter, discard sequences with
more than the specified number of bases.
--fastq_maxmergelen positive integer
When using --fastq_mergepairs, specify the maximum length of the merged sequence.
By default there is no limit.
--fastq_maxns positive integer
When using --fastq_filter, --fastq_mergepairs or --fastx_filter, discard sequences with
more than the specified number of N’s.
--fastq_mergepairs filename
Merge paired-end sequence reads into one sequence. The forward reads are specified as
the argument to this option and the reverse reads are specified with the --reverse option.
The merged sequences are output to the file(s) specified with the --fastaout or --fastqout
options. The non-merged reads can be output to the files specified with the --fastaout_notmerged_fwd, --fastaout_notmerged_rev, --fastqout_notmerged_fwd and
--fastqout_notmerged_rev options. Statistics may be output to the file specified with the
--eetabbedout option. Sequences are truncated as specified with the --fastq_truncqual
option to remove low-quality bases in the 3’ end. Sequences shorter than specified with
--fastq_minlen (after truncation) are discarded (1 by default). Sequences with too many
ambiguous bases (N’s), as specified with the --fastq_maxns are also discarded (no limit
by default). Staggered reads are not merged unless the --fastq_allowmergestagger
option is specified. The minimum length of the overlap region between the reads may
be specified with the --fastq_minovlen option (default 10). The overlap region may not
include more mismatches than specified with the --fastq_maxdiffs option (10 by
default) or a higher percentage of mismatches than specified with the --fastq_maxdiffpct option (100.0% by default), otherwise the read pair is discarded. Additional rules
will avoid merging of reads that cannot be aligned reliably and unambiguously. The
mimimum and maximum length of the merged sequence may be specified with the
--fastq_minmergelen and --fastq_maxmergelen options, respectively. Other relevant
options are: --fastq_ascii, --fastq_maxee, --fastq_nostagger, --fastq_qmax,
--fastq_qmaxout, --fastq_qmin, --fastq_qminout, and --label_suffix.
--fastq_minlen positive integer
When using --fastq_filter, --fastq_mergepairs or --fastx_filter, discard sequences with
less than the specified number of bases (default 1).
--fastq_minmergelen positive integer
When using --fastq_mergepairs, specify the minimum length of the merged sequence.
The default is 1.
--fastq_minovlen positive integer
When using --fastq_mergepairs, specify the minimum overlap between the merged
reads. The default is 10.
--fastq_nostagger
When using --fastq_mergepairs, forbid the merging of staggered read pairs. This is the
default behaviour of --fastq_mergepairs. To change that behaviour, see the
--fastq_allowmergestagger option.
--fastq_qmax positive integer
Specify the maximum quality score accepted when reading FASTQ files. The default is
41, which is usual for recent Sanger/Illumina 1.8+ files.
--fastq_qmaxout positive integer
When using --fastq_convert or --sff_convert, specify the maximum quality score used
when writing FASTQ files. The default is 41, which is usual for recent Sanger/Illumina
1.8+ files. Older formats may use a maximum quality score of 40.

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--fastq_qmin positive integer
Specify the minimum quality score accepted for FASTQ files. The default is 0, which is
usual for recent Sanger/Illumina 1.8+ files. Older formats may use scores between -5
and 2.
--fastq_qminout positive integer
When using --fastq_convert or --sff_convert, specify the minimum quality score used
when writing FASTQ files. The default is 0, which is usual for Sanger/Illumina 1.8+
files. Older versions of the format may use scores between -5 and 2.
--fastq_stats filename
Analyze a FASTQ file and report the number of reads it contains. The quality encoding
and the range of quality values may be specified with --fastq_ascii --fastq_qmin and
--fastq_qmax. That command requires the --log option and outputs the following
detailed statistics on read length, quality score, length vs. quality distributions, and
length / quality filtering:
Read length distribution:
1.

L: read length.

N: number of reads.

Pct: fraction of reads with this length.

AccPct: fraction of reads with this length or longer.

Quality score distribution:
1.

ASCII: character encoding the quality score.

Q: Phred quality score.

Pe: probability of error associated with the quality score.

N: number of bases with this quality score.

Pct: fraction of bases with this quality score.

AccPct: fraction of bases with this quality score or higher.

Length vs. quality distribution:
1.

L: position in reads (starting from position 2).

PctRecs: fraction of reads with at least this length.

AvgQ: average quality score over all reads up to this position.

P(AvgQ): error probability corresponding to AvgQ.

AvgP: average error probability.

AvgEE: average expected error over all reads up to this position.

Rate: growth rate of AvgEE between this position and position - 1.

RatePct: Rate (as explained above) expressed as a percentage.

Effect of expected error and length filtering:
The first column indicates read lengths (L). The next four columns indicate the
number of reads that would be retained by the --fastq_filter command if the
reads were truncated at length L (option --fastq_trunclen L) and filtered to
have a maximum expected error of 1.0, 0.5, 0.25 or 0.1 (with the option
--fastq_maxee float). The last four columns indicate the fraction of reads that
would be retained by the --fastq_filter command using the same length and
maximum expected error parameters.

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Effect of minimum quality and length filtering:
The first column indicates read lengths (Len). The next four columns indicate
the fraction of reads that would be retained by the --fastq_filter command if
the reads were truncated at length Len (option --fastq_trunclen Len) or at the
first position with a quality Q below 5, 10, 15 or 20 (option --fastq_truncqual
Q).
--fastq_stripleft positive integer
When using --fastq_filter or --fastx_filter, strip the specified number of bases from the
left end of the reads.
--fastq_stripright positive integer
When using --fastq_filter or --fastx_filter, strip the specified number of bases from the
right end of the reads.
--fastq_tail positive integer
When using --fastq_chars, count the number of times a series of characters of length k
appears at the end of quality strings. By default, k = 4.
--fastq_truncee real
When using --fastq_filter or --fastx_filter, truncate sequences so that their total
expected error is not higher than the specified value.
--fastq_trunclen positive integer
When using --fastq_filter or --fastx_filter, truncate sequences to the specified length.
Shorter sequences are discarded.
--fastq_trunclen_keep positive integer
When using --fastq_filter or --fastx_filter, truncate sequences to the specified length.
Shorter sequences are not discarded.
--fastq_truncqual positive integer
When using --fastq_filter or --fastx_filter, truncate sequences starting from the first base
with the specified base quality score value or lower.
--fastqout filename
When using --fastq_filter, --fastq_mergepairs or --fastx_filter, write to the given
FASTQ-formatted file the sequences passing the filter, or the merged sequences.
--fastqout_discarded filename
When using --fastq_filter or --fastx_filter, write sequences that do not pass the filter to
the given FASTQ-formatted file.
--fastqout_notmerged_fwd filename
When using --fastq_mergepairs, write forward reads not merged to the specified
FASTQ file.
--fastqout_notmerged_rev filename
When using --fastq_mergepairs, write reverse reads not merged to the specified FASTQ
file.
--fastx_filter filename
Shorten and/or filter the sequences in the given FASTA or FASTQ file and output the
remaining sequences to the FASTQ file specified with the --fastqout option and to the
FASTA file specified with the --fastaout option. The discarded sequences are written to
the files specified with the --fastaout_discarded and --fastqout_discarded options. The
input format (FASTA or FASTQ) is automatically detected. Output can not be written
to FASTQ files if the input is in FASTA format. Sequences may be shortened using the
options --fastq_stripleft, --fastq_stripright, --fastq_truncee, --fastq_trunclen,
--fastq_trunclen_keep and --fastq_truncqual. The sequences may be filtered using the
options
--fastq_maxee,
--fastq_maxee_rate,
--fastq_maxlen,
--fastq_maxns,
--fastq_minlen, --fastq_trunclen, --maxsize, and --minsize. If shortening results in an

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empty sequence, it is discarded. The sequences are first shortened and then filtered
based on the remaining bases. If no shortening or filtering options are given, all
sequences are written to the output files, possibly after conversion from FASTQ to
FASTA format. The --relabel option may be used to relabel the output sequences. The
--eeout may be used to output the expected number of errors in each sequence.
--fastx_revcomp filename
Reverse-complement the sequences in the given FASTA or FASTQ file to a file specified with the --fastaout and/or --fastqout options. If the input file is in FASTA format,
the output can not be written back to a FASTQ file due to missing base quality scores.
--join_padgap string
When running --fastq_join, use the string as a sequence padding string. The default is
NNNNNNNN (8 N’s).
--join_padgapq string
When running --fastq_join, use the string as a quality padding string. The default is a
string of I’s equal in length to the sequence padding string. The letter I corresponds to a
base quality score of 40 indicating a very high quality base with error probability of
0.0001.
--label_suffix string
When using --fastx_revcomp or --fastq_mergepairs, add the suffix string to sequence
headers.
--maxsize positive integer
When using --fastq_filter or --fastx_filter, discard sequences with an abundance higher
than the specified value.
--minsize positive integer
When using --fastq_filter or --fastx_filter, discard sequences with an abundance lower
than the specified value.
--output filename
When using --fastq_eestats or --fastq_eestats2, write tabulated results to filename. See
--fastq_eestats’s and --fastq_eestats2’s documentation for a complete description of the
table.
--relabel_keep
When using --relabel, keep the old identifier in the header after a space.
--relabel string
Please see the description of the same option under Chimera detection for details.
--relabel_md5
Please see the description of the same option under Chimera detection for details.
--relabel_sha1
Please see the description of the same option under Chimera detection for details.
--reverse filename
When using --fastq_mergepairs or --fastq_join, specify the FASTQ file containing containing the reverse reads.
--sff_convert filename
Convert the given SFF file to FASTQ. The FASTQ output file is specified with the
--fastqout option. The sequence may be clipped as specified in the SFF file if the option
--sff_clip is specified, otherwise no clipping occurs. Bases that would have been
clipped are converted to lower case, while the rest is in upper case. The output quality
encoding may be specified with the --fastq_asciiout option (default 33). The minimum
and maximum output quality scores may be limited using the --fastq_qminout and
--fastq_qmaxout options.

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--sff_clip Specifies that the sequences converted by the --sff_convert command should be clipped
in both ends as indicated in the SFF file. By default no clipping is performed.
--xsize

Strip abundance information from the headers when writing the output file.

Masking options:
An input sequence can be composed of lower- or uppercase letters. When soft masking is specified, lower case letters are treated as symbols that should be masked. Otherwise the case of the
input sequences is ignored.
Masking is performed by the commands for chimera detection (uchime_denovo, uchime_ref),
clustering (cluster_fast, cluster_smallmem, cluster_size), masking (maskfasta, fastx_mask), pairwise alignment (allpairs_global) and searching (search_exact, usearch_global).
Masking is usually specified with the --qmask option, while the --dbmask option is used for the
database sequences specified with the --db option with the --usearch_global, --search_exact and
--uchime_ref commands.
The argument to the --qmask and --dbmask option may be none, soft or dust. If the argument is
none, the no masking is performed. If the argument is soft the lower case symbols are masked.
Finally, if the argument is dust, the sequence is masked using the DUST algorithm by Tatusov and
Lipman to mask low-complexity regions.
If the --hardmask option is specified, all masked regions are converted to N’s, otherwise masked
regions are indicated by lower case letters.
If any sequence is masked, the masked version of the sequence (with lower case letters or N’s) is
used in all output files. Otherwise the sequence is unmodified. The exception is the sequences in
the output file specified with the --uchimealns option, where the input sequences are converted to
upper case first and lower case letters indicate disagreement between the aligned sequences.
When a sequence region is masked, words in the region are not included in the indices used in the
heuristic search algorithm. In all other aspects, the region is treated as other regions.
Regions in sequences that are hardmasked (with N’s) have a zero alignment score and do not contribute to an alignment.
Here are the results of combined masking options --qmask (or --dbmask for database sequences)
and --hardmask, assuming each input sequence contains both lower and uppercase nucleotides:
qmask
none
none
dust
dust
soft
soft

hardmask
off
on
off
on
off
on

action
no masking, all symbols used, no change
no masking, all symbols used, no change
masked symbols lowercased, rest uppercased
masked symbols changed to Ns, rest unchanged
lowercase symbols masked, no case changes
lowercase symbols masked and changed to Ns

--fastaout filename
Write the masked sequences to filename, in fasta format. Applies only to the
--fastx_mask command.
--fastqout filename
Write the masked sequences to filename, in fastq format. Applies only to the
--fastx_mask command.
--fastx_mask filename
Mask regions in sequences contained in the specified fasta or fastq file. The default is
to mask using DUST (use --qmask to modify that behavior). The output files are specified with the --fastaout and --fastqout options. The minimum and maximum percentage
of unmasked residues may be specified with the --min_unmasked_pct and
--max_unmasked_pct options, respectively.
--hardmask
Symbols in masked regions are replaced by N’s. The default is to replace the masked
regions by lower case letters.

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--maskfasta filename
Mask regions in sequences contained in the fasta file filename. The default is to mask
using dust (use --qmask to modify that behavior). The output file is specified with the
--output option. This command is depreciated, please use --fastx_mask instead.
--max_unmasked_pct real
Discard sequences with more than the specified maximum percentage of unmasked
residues. Works only with --fastx_mask.
--min_unmasked_pct real
Discard sequences with less than the specified minimum percentage of unmasked
residues. Works only with --fastx_mask.
--output filename
Write the masked sequences to filename, in fasta format. Applies only to the
--mask_fasta command.
--qmask none|dust|soft
If the argument is dust, mask regions in sequences using the DUST algorithm that
detects simple repeats and low-complexity regions. This is the default. If the argument
is soft, mask the lower case letters in the input sequence. If the argument is none, do
not mask.
Pairwise alignment options:
The results of the n * (n - 1) / 2 pairwise alignments are written to the result files specified with
--alnout, --blast6out, --fastapairs --matched, --notmatched, --samout, --uc or --userout (see Searching section below). Specify either the --acceptall option to output all pairwise alignments, or specify an identity level with --id to discard weak alignments. Most other accept/reject options (see
Searching options below) may also be used. Sequences are aligned on their plus strand only.
Masking is performed as usual and specified with --qmask and --hardmask.
--acceptall
Write the results of all alignments to output files. This option overrides all other
accept/reject options (including --id).
--allpairs_global filename
Perform optimal global pairwise alignments of all vs. all fasta sequences contained in
filename. This command is multi-threaded.
--id real Reject the sequence match if the pairwise identity is lower than real (value ranging
from 0.0 to 1.0 included).
--threads positive integer
Number of computation threads to use (1 to 256). The number of threads should be
lesser or equal to the number of available CPU cores. The default is to use all available
resources and to launch one thread per logical core.
--uc filename
Output pairwise alignment results in filename using a tab-separated uclust-like format
with 10 columns. Each sequence is compared to all other sequences, and all hits
(--acceptall) or only some hits (--id float) are reported, with one pairwise comparison
per line:

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Record type, always set to ’H’.

Ordinal number of the target sequence (based on input order, starting
from zero).

Sequence length.

Percentage of similarity with the target sequence.

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Match orientation, always set to ’+’.

Not used, always set to zero.

Compact representation of the pairwise alignment using the CIGAR format (Compact Idiosyncratic Gapped Alignment Report): M (match), D
(deletion) and I (insertion). The equal sign ’=’ indicates that the query is
identical to the centroid sequence.

Label of the query sequence.

10. Label of the target sequence.
Searching options:
--alnout filename
Write pairwise global alignments to filename using a human-readable format. Use
--rowlen to modify alignment length. Output order may vary when using multiple
threads.
--biomout filename
Write search results to an OTU table in the biom version 1.0 file format. The query file
contains the samples, while the database file contains the OTUs. Sample and OTU
identifiers are extracted from the header of these sequences. See the --biomout option
in the Clustering section for further details.
--blast6out filename
Write search results to filename using a blast-like tab-separated format of twelve fields
(listed below), with one line per query-target matching (or lack of matching if --output_no_hits is used). Warning, vsearch uses global pairwise alignments, not blast’s
seed-and-extend algorithm. Therefore, some common blast output values (alignment
start and end, evalue, bit score) are reported differently. Output order may vary when
using multiple threads. A similar output can be obtain with --userout filename and
--userfields query+target+id+alnlen+mism+opens+qlo+qhi+tlo+thi+evalue+bits. A
complete list and description is available in the section ’Userfields’ of this manual.

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query: query label.

target: target (database sequence) label. The field is set to ’*’ if there is
no alignment.

id: percentage of identity (real value ranging from 0.0 to 100.0). The percentage identity is defined as 100 * (matching columns) / (alignment
length - terminal gaps). See fields id0 to id4 for other definitions.

alnlen: length of the query-target alignment (number of columns). The
field is set to 0 if there is no alignment.

mism: number of mismatches in the alignment (zero or positive integer
value).

opens: number of columns containing a gap opening (zero or positive
integer value).

qlo: first nucleotide of the query aligned with the target. Always equal to
1 if there is an alignment, 0 otherwise (see qilo to ignore initial gaps).

qhi: last nucleotide of the query aligned with the target. Always equal to
the length of the pairwise alignment, 0 otherwise (see qihi to ignore terminal gaps).

tlo: first nucleotide of the target aligned with the query. Always equal to
1 if there is an alignment, 0 otherwise (see tilo to ignore initial gaps).

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10. thi: last nucleotide of the target aligned with the query. Always equal to
the length of the pairwise alignment, 0 otherwise (see tihi to ignore terminal gaps).
11. evalue: expectancy-value (not computed for nucleotide alignments).
Always set to -1.
12. bits: bit score (not computed for nucleotide alignments). Always set to 0.
--db filename
Compare query sequences (specified with --usearch_global) to the fasta-formatted target sequences contained in filename, using global pairwise alignment. Alternatively, the
name of a preformatted UDB database created using the makeudb_usearch command
(see below) may be specified.
--dbmask none|dust|soft
Mask regions in the target database sequences using the dust method or the soft
method, or do not mask (none). Warning, when using soft masking search commands
become case sensitive. The default is to mask using dust.
--dbmatched filename
Write database target sequences matching at least one query sequence to filename, in
fasta format. If the option --sizeout is used, the number of queries that matched each
target sequence is indicated using the pattern ";size=integer;".
--dbnotmatched filename
Write database target sequences not matching query sequences to filename, in fasta format.
--fastapairs filename
Write pairwise alignments of query and target sequences to filename, in fasta format.
--fulldp

Dummy option for compatibility with usearch. To maximize search sensitivity, vsearch
uses a 8-way 16-bit SIMD vectorized full dynamic programming algorithm (Needleman-Wunsch), whether or not --fulldp is specified.

--gapext string
Set penalties for a gap extension. See --gapopen for a complete description of the
penalty declaration system. The default is to initialize the six gap extending penalties
using a penalty of 2 for extending internal gaps and a penalty of 1 for extending terminal gaps, in both query and target sequences (i.e. 2I/1E).
--gapopen string
Set penalties for a gap opening. A gap opening can occur in six different contexts: in
the query (Q) or in the target (T) sequence, at the left (L) or right (R) extremity of the
sequence, or inside the sequence (I). Sequence symbols (Q and T) can be combined
with location symbols (L, I, and R), and numerical values to declare penalties for all
possible contexts: aQL/bQI/cQR/dTL/eTI/fTR, where abcdef are zero or positive integers, and ’/’ is used as a separator.
To simplify declarations, the location symbols (L, I, and R) can be combined, the symbol (E) can be used to treat both extremities (L and R) equally, and the symbols Q and
T can be omitted to treat query and target sequences equally. For instance, the default is
to declare a penalty of 20 for opening internal gaps and a penalty of 2 for opening terminal gaps (left or right), in both query and target sequences (i.e. 20I/2E). If only a
numerical value is given, without any sequence or location symbol, then the penalty
applies to all gap openings. To forbid gap-opening, an infinite penalty value can be
declared with the symbol ’*’. To use vsearch as a semi-global aligner, a null-penalty
can be applied to the left (L) or right (R) gaps.
vsearch always initializes the six gap opening penalties using the default parameters
(20I/2E). The user is then free to declare only the values he/she wants to modify. The

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string is scanned from left to right, accepted symbols are (0123456789/LIREQT*), and
later values override previous values.
Please note that vsearch, in contrast to usearch, only allows integer gap penalties.
Because the lowest gap penalties are 0.5 by default in usearch, all default scores and
gap penalties in vsearch have been doubled to maintain equivalent penalties and to produce identical alignments.
--hardmask
Mask sequence regions by replacing them with Ns instead of setting them to lower case
as is the default. For more information, please see the Masking section.
--id real Reject the sequence match if the pairwise identity is lower than real (value ranging
from 0.0 to 1.0 included). The search process sorts target sequences by decreasing
number of k-mers they have in common with the query sequence, using that information as a proxy for sequence similarity. That efficient pre-filtering also prevents pairwise alignments with weakly matching targets, as there needs to be at least 6 shared kmers to start the pairwise alignment, and at least one out of every 16 k-mers from the
query needs to match the target. Consequently, using values lower than --id 0.5 is not
likely to capture more weakly matching targets. The pairwise identity is by default
defined as the number of (matching columns) / (alignment length - terminal gaps). That
definition can be modified by --iddef.
--iddef 0|1|2|3|4
Change the pairwise identity definition used in --id. Values accepted are:
0.

CD-HIT definition: (matching columns) / (shortest sequence length).

edit distance: (matching columns) / (alignment length).

edit distance excluding terminal gaps (default definition for --id).

BLAST definition, equivalent to --iddef 1 for global pairwise alignments.

The option --userfields accepts the fields id0 to id4, in addition to the field id, to report
the pairwise identity values corresponding to the different definitions.
--idprefix positive integer
Reject the sequence match if the first integer nucleotides of the target do not match the
query.
--idsuffix positive integer
Reject the sequence match if the last integer nucleotides of the target do not match the
query.
--leftjust Reject the sequence match if the pairwise alignment begins with gaps.
--match integer
Score assigned to a match (i.e. identical nucleotides) in the pairwise alignment. The
default value is 2.
--matched filename
Write query sequences matching database target sequences to filename, in fasta format.
--maxaccepts positive integer
Maximum number of hits to accept before stopping the search. The default value is 1.
This option works in pair with --maxrejects. The search process sorts target sequences
by decreasing number of k-mers they have in common with the query sequence, using
that information as a proxy for sequence similarity. After pairwise alignments, if the
first target sequence passes the acceptation criteria, it is accepted as best hit and the

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search process stops for that query. If --maxaccepts is set to a higher value, more hits
are accepted. If --maxaccepts and --maxrejects are both set to 0, the complete database
is searched.
--maxdiffs positive integer
Reject the sequence match if the alignment contains at least integer substitutions, insertions or deletions.
--maxgaps positive integer
Reject the sequence match if the alignment contains at least integer insertions or deletions.
--maxhits positive integer
Maximum number of hits to show once the search is terminated (hits are sorted by
decreasing identity). Unlimited by default. That option applies to --alnout, --blast6out,
--fastapairs, --samout, --uc, or --userout output files.
--maxid real
Reject the sequence match if the percentage of identity between the two sequences is
greater than real.
--maxqsize positive integer
Reject query sequences with an abundance greater than integer.
--maxqt real
Reject if the query/target sequence length ratio is greater than real.
--maxrejects positive integer
Maximum number of non-matching target sequences to consider before stopping the
search. The default value is 32. This option works in pair with --maxaccepts. The
search process sorts target sequences by decreasing number of k-mers they have in
common with the query sequence, using that information as a proxy for sequence similarity. After pairwise alignments, if none of the first 32 examined target sequences pass
the acceptation criteria, the search process stops for that query (no hit). If --maxrejects
is set to a higher value, more target sequences are considered. If --maxaccepts and
--maxrejects are both set to 0, the complete database is searched.
--maxsizeratio real
Reject if the query/target abundance ratio is greater than real.
--maxsl real
Reject if the shorter/longer sequence length ratio is greater than real.
--maxsubs positive integer
Reject the sequence match if the pairwise alignment contains more than integer substitutions.
--mid real
Reject the sequence match if the percentage of identity is lower than real (ignoring all
gaps, internal and terminal).
--mincols positive integer
Reject the sequence match if the alignment length is shorter than integer.
--minqt real
Reject if the query/target sequence length ratio is lower than real.
--minsizeratio real
Reject if the query/target abundance ratio is lower than real.
--minsl real
Reject if the shorter/longer sequence length ratio is lower than real.

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--mintsize positive integer
Reject target sequences with an abundance lower than integer.
--minwordmatches non-negative integer
Minimum number of word matches required for a sequence to be considered further.
Default value is 12 for the default word length 8. For word lengths 3-15, the default
minimum word matches are 18, 17, 16, 15, 14, 12, 11, 10, 9, 8, 7, 5 and 3, respectively.
If the query sequence has fewer unique words than the number specified, all words in
the query must match. If the argument is 0, no word matches are required.
--mismatch integer
Score assigned to a mismatch (i.e. different nucleotides) in the pairwise alignment. The
default value is -4.
--mothur_shared_out filename
Write search results to an OTU table in the mothur ’shared’ tab-separated plain text file
format. The query file contains the samples, while the database file contains the OTUs.
Sample and OTU identifiers are extracted from the header of these sequences. See the
--otutabout option in the Clustering section for further details.
--notmatched filename
Write query sequences not matching database target sequences to filename, in fasta format.
--otutabout filename
Write search results to an OTU table in the classic tab-separated plain text format. The
query file contains the samples, while the database file contains the OTUs. Sample and
OTU identifiers are extracted from the header of these sequences. See the
--mothur_shared_out option in the Clustering section for further details.
--output_no_hits
Write both matching and non-matching queries to --alnout, --blast6out, --samout or
--userout output files. Non-matching queries are labelled ’No hits’ in --alnout files.
--pattern string
This option is ignored. It is provided for compatibility with usearch.
--qmask none|dust|soft
Mask regions in the query sequences using the dust or the soft algorithms, or do not
mask (none). Warning, when using soft masking search commands become case sensitive. The default is to mask using dust.
--query_cov real
Reject if the fraction of the query aligned to the target sequence is lower than real. The
query coverage is computed as (matches + mismatches) / query sequence length. Internal or terminal gaps are not taken into account.
--rightjust
Reject the sequence match if the pairwise alignment ends with gaps.
--rowlen positive integer
Width of alignment lines in --alnout output. The default value is 64. Set to 0 to eliminate wrapping.
--samheader
Include header lines to the SAM file when --samout is specified. The header includes
lines starting with @HD, @SQ and @PG, but no @RG lines (see
). By default no header line is written.
--samout filename
Write alignment results to filename using the SAM format (a tab-separated text file).
When using the --samheader option, the SAM file starts with header lines. Each non-

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header line is a SAM record, which represents either a query-target alignment or the
absence of match for a query (output order may vary when using multiple threads).
Each record contains 11 mandatory fields and optional fields (see
for a complete description of the format):
1.

query sequence label.

combination of bitwise flags. Possible values are: 0 (top hit), 4 (no hit),
16 (reverse-complemented hit), 256 (secondary hit, i.e. all hits except the
top hit).

target sequence label.

first position of a target aligned with the query (always 1 for global pairwise alignments, 0 if there is no match).

mapping quality (ignored, always set to ’*’).

CIGAR string (set to ’*’ if there is no match).

name of the target sequence matching with the next read of the query (for
mate reads only, ignored and always set to ’*’).

position of the primary alignment of the next read of the query (for mate
reads only, ignored and always set to 0).

target sequence length (for multi-segment targets, ignored and always set
to 0).

10. query sequence (complete, not only the segment aligned to the target as
usearch does).
11. quality string (ignored, always set to ’*’).
Optional fields for query-target matches (number and order of fields
may vary):
12. AS:i:? alignment score (i.e. percentage of identity).
13. XN:i:? next best alignment score (always set to 0).
14. XM:i:? number of mismatches.
15. XO:i:? number of gap openings (excluding terminal gaps).
16. XG:i:? number of gap extensions (excluding terminal gaps).
17. NM:i:? edit distance to the target (sum of XM and XG).
18. MD:Z:? string for mismatching positions.
19. YT:Z:UU string representing the alignment type.
--search_exact filename
Search for exact full-length matches to the query sequences contained in filename in
the database of target sequences (--db). Only 100% exact matches are reported and this
command is much faster than --usearch_global. The --id, --maxaccepts and --maxrejects options are ignored, but the rest of the searching options may be specified.
--self

Reject the sequence match if the query and target labels are identical.

--selfid

Reject the sequence match if the query and target sequences are strictly identical.

--sizeout Add abundance annotations to the output of the option --dbmatched (using the pattern
’;size=integer;’), to report the number of queries that matched each target.
--strand plus|both
When searching for similar sequences, check the plus strand only (default) or check
both strands.

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--target_cov real
Reject the sequence match if the fraction of the target sequence aligned to the query
sequence is lower than real. The target coverage is computed as (matches + mismatches) / target sequence length. Internal or terminal gaps are not taken into account.
--top_hits_only
Only the top hits between the query and database sequence sets are written to the output specified with the options --alnout, --samout, --userout, --blast6out, --uc,
--fastapairs, --matched or --notmatched (but not --dbmatched and --dbnotmatched). For
each query, the top hit is the one presenting the highest percentage of identity (see the
--iddef option to change the way identity is measured). For a given query, if several top
hits present exactly the same percentage of identity, the number of hits reported is controlled by the --maxaccepts value (1 by default).
--uc filename
Output searching results in filename using a tab-separated uclust-like format with 10
columns. When using the --search_exact command, the table layout is the same than
with the --allpairs_global. When using the --usearch_global command, the table
present two different type of entries: hit (H) or no hit (N). Each query sequence is compared to all other sequences, and the best hit (--maxaccept 1) or several hits (--maxaccept > 1) are reported (H). Output order may vary when using multiple threads. Column content varies with the type of entry (H or N):
1.

Record type: H, or N (’hit’ or ’no hit’).

Ordinal number of the target sequence (based on input order, starting
from zero). Set to ’*’ for N.

Sequence length. Set to ’*’ for N.

Percentage of similarity with the target sequence. Set to ’*’ for N.

Match orientation + or -. . Set to ’.’ for N.

Not used, always set to zero for H, or ’*’ for N.

Label of the query sequence.

10. Label of the target centroid sequence. Set to ’*’ for N.
--uc_allhits
When using the --uc option, show all hits, not just the top hit for each query.
--usearch_global filename
Compare target sequences (--db) to the fasta-formatted query sequences contained in
filename, using global pairwise alignment.
--userfields string
When using --userout, select and order the fields written to the output file. Fields are
separated by ’+’ (e.g. query+target+id). See the ’Userfields’ section for a complete list
of fields.
--userout filename
Write user-defined tab-separated output to filename. Select the fields with the option
--userfields. Output order may vary when using multiple threads. If --userfields is
empty or not present, filename is empty.

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--weak_id real
Show hits with percentage of identity of at least real, without terminating the search. A
normal search stops as soon as enough hits are found (as defined by --maxaccepts,
--maxrejects, and --id). As --weak_id reports weak hits that are not deduced from
--maxaccepts, high --id values can be used, hence preserving both speed and sensitivity.
Logically, real must be smaller than the value indicated by --id.
--wordlength positive integer
Length of words (i.e. k-mers) for database indexing. The range of possible values goes
from 3 to 15, but values near 8 or 9 are generally recommended. Longer words may
reduce the sensitivity/recall for weak similarities, but can increase precision. On the
other hand, shorter words may increase sensitivity or recall, but may reduce precision.
Computation time generally increases with shorter words and decreases with longer
words, but it increases again for very long words. Memory requirements for a part of
the index increase with a factor of 4 each time word length increases by one nucleotide,
and this generally becomes significant for long words (12 or more). The default value is
8.
Shuffling options:
Fasta entries in the input file are outputted in a pseudo-random order.
--output filename
Write the shuffled sequences to filename, in fasta format.
--randseed positive integer
When shuffling sequence order, use integer as seed. A given seed always produces the
same output order (useful for replicability). Set to 0 to use a pseudo-random seed
(default behavior).
--relabel string
Relabel sequences using the prefix string and a ticker (1, 2, 3, etc.) to construct the new
headers. Use --sizeout to conserve the abundance annotations.
--relabel_keep
When relabelling, keep the old identifier in the header after a space.
--relabel_md5
Relabel sequences using the MD5 message digest algorithm applied to each sequence.
Former sequence headers are discarded. The sequence is converted to upper case and U
is replaced by T before the digest is computed. The MD5 digest is a cryptographic hash
function designed to minimize the probability that two different inputs gives the same
output, even for very similar, but non-identical inputs. Still, there is always a very
small, but non-zero probability that two different inputs give the same result. The MD5
digest generates a 128-bit (16-byte) digest that is represented by 16 hexadecimal numbers (using 32 symbols among 0123456789abcdef). Use --sizeout to conserve the abundance annotations.
--relabel_sha1
Relabel sequences using the SHA1 message digest algorithm applied to each sequence.
It is similar to the --relabel_md5 option but uses the SHA1 algorithm instead of the
MD5 algorithm. The SHA1 digest generates a 160-bit (20-byte) result that is represented by 20 hexadecimal numbers (40 symbols). The probability of a collision (two
non-identical sequences having the same digest) is smaller for the SHA1 algorithm
than it is for the MD5 algorithm. Use --sizeout to conserve the abundance annotations.
--sizeout When using --relabel, --relabel_md5 or --relabel_sha1, preserve and report abundance
annotations to the output fasta file (using the pattern ’;size=integer;’).

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--shuffle filename
Pseudo-randomly shuffle the order of sequences contained in filename.
--topn positive integer
Output only the first integer sequences after pseudo-random reordering.
--xsize

Strip abundance information from the headers when writing the output file.

Sorting options:
Fasta entries are sorted by decreasing abundance (--sortbysize) or sequence length (--sortbylength). To obtain a stable sorting order, ties are sorted by decreasing abundance and label
increasing alpha-numerical order (--sortbylength), or just by label increasing alpha-numerical
order (--sortbysize). Label sorting assumes that all sequences have unique labels. The same applies
to the automatic sorting performed during chimera checking (--uchime_denovo), dereplication
(--derep_fulllength), and clustering (--cluster_fast and --cluster_size).
--maxsize positive integer
When using --sortbysize, discard sequences with an abundance value greater than integer.
--minsize positive integer
When using --sortbysize, discard sequences with an abundance value smaller than integer.
--output filename
Write the sorted sequences to filename, in fasta format.
--relabel string
Please see the description of the same option under Chimera detection for details.
--relabel_keep
When relabelling, keep the old identifier in the header after a space.
--relabel_md5
Please see the description of the same option under Chimera detection for details.
--relabel_sha1
Please see the description of the same option under Chimera detection for details.
--sizeout When using --relabel, report abundance annotations to the output fasta file (using the
pattern ’;size=integer;’).
--sortbylength filename
Sort by decreasing length the sequences contained in filename. See the general options
--minseqlength and --maxseqlength to eliminate short and long sequences.
--sortbysize filename
Sort by decreasing abundance the sequences contained in filename (missing abundance
values are assumed to be ’;size=1’). See the options --minsize and --maxsize to eliminate rare and dominant sequences.
--topn positive integer
Output only the top integer sequences (i.e. the longest or the most abundant).
--xsize

Strip abundance information from the headers when writing the output file.

Subsampling options:
Subsampling randomly extracts a certain number or a certain percentage of the sequences in the
input file. If the --sizein option is in effect, the abundances of the input sequences is taken into
account and the sampling is performed as if the input sequences were rereplicated, subsampled
and dereplicated before being written to the output file. The extraction is performed as a random
sampling with a uniform distribution among the input sequences and is performed without replacement. The input file is specified with --fastx_subsample option, the output files are specified with
the --fastaout and --fastqout options and the amount of sequences to be sampled is specified with

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the --sample_pct or --sample_size options. The sequences not sampled may be written to files
specified with the options --fasta_discarded and --fastq_discarded. The --fastq_ascii, --fastq_qmin
and --fastq_qmax options are also available.
--fastaout filename
Write the sampled sequences to filename, in fasta format.
--fastaout_discarded filename
Write the sequences not sampled to filename, in fasta format.
--fastq_ascii positive integer
Define the ASCII character number used as the basis for the FASTQ quality score. The
default is 33, which is used by the Sanger / Illumina 1.8+ FASTQ format (phred+33).
The value 64 is used by the Solexa, Illumina 1.3+ and Illumina 1.5+ formats
(phred+64).
--fastq_qmax positive integer
Specify the maximum quality score accepted when reading FASTQ files. The default is
41, which is usual for recent Sanger/Illumina 1.8+ files.
--fastq_qmin positive integer
Specify the minimum quality score accepted for FASTQ files. The default is 0, which is
usual for recent Sanger/Illumina 1.8+ files. Older formats may use scores between -5
and 2.
--fastqout filename
Write the sampled sequences to filename, in fastq format. Requires input in fastq format.
--fastqout_discarded filename
Write the sequences not sampled to filename, in fastq format. Requires input in fastq
format.
--fastx_subsample filename
Perform subsampling from the sequences in the specified input file that is in FASTA or
FASTQ format.
--randseed positive integer
Use integer as a seed for the pseudo-random generator. A given seed always produces
the same output, which is useful for replicability. Set to 0 to use a pseudo-random seed
(default behavior).
--relabel string
Relabel sequences using the prefix string and a ticker (1, 2, 3, etc.) to construct the new
headers. Use --sizeout to conserve the abundance annotations.
--relabel_keep
When relabelling, keep the old identifier in the header after a space.
--relabel_md5
Relabel sequences using the MD5 message digest algorithm applied to each sequence.
Former sequence headers are discarded. The sequence is converted to upper case and U
is replaced by T before the digest is computed. The MD5 digest is a cryptographic hash
function designed to minimize the probability that two different inputs give the same
output, even for very similar, but non-identical inputs. Still, there is always a very
small, but non-zero probability that two different inputs give the same result. The MD5
digest generates a 128-bit (16-byte) digest that is represented by 16 hexadecimal numbers (using 32 symbols among 0123456789abcdef). Use --sizeout to conserve the abundance annotations.

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--relabel_sha1
Relabel sequences using the SHA1 message digest algorithm applied to each sequence.
It is similar to the --relabel_md5 option but uses the SHA1 algorithm instead of the
MD5 algorithm. The SHA1 digest generates a 160-bit (20-byte) result that is represented by 20 hexadecimal numbers (40 symbols). The probability of a collision (two
non-identical sequences having the same digest) is smaller for the SHA1 algorithm
than it is for the MD5 algorithm. Use --sizeout to conserve the abundance annotations.
--sample_pct real
Subsample the given percentage of the input sequences. Accepted values range from
0.0 to 100.0.
--sample_size positive integer
Extract the given number of sequences.
--sizein

Take the abundance information of the input file into account, otherwise the abundance
of each sequence is considered to be 1.

--sizeout Write abundance information to the output file.
--xsize

Strip abundance information from the headers when writing the output file.

Taxonomic classification options:
The vsearch command --sintax will classify the input sequences according to the Sintax algorithm
as described by Robert Edgar (2016) in SINTAX: a simple non-Bayesian taxonomy classifier for
16S and ITS sequences, BioRxiv, 074161. Preprint. doi: https://doi.org/10.1101/074161.
The name of the fasta file containing the input sequences to be classified is given as an argument to
the --sintax command. The reference sequence database is specified with the --db option. The
results are written in a tab delimited text file whose name is specified with the --tabbedout option.
The --sintax_cutoff option may be used to set a minimum level of bootstrap support for the taxonomic ranks to be reported.
Multithreading is supported. Databases in UDB files are supported. The strand option may be
specified.
The reference database must contain taxonomic information in the header of each sequence in the
form of a string starting with ";tax=" and followed by a comma-separated list of up to eight taxonomic identifiers. Each taxonomic identifier must start with an indication of the rank by one of the
letters d (for domain) k (kingdom), p (phylum), c (class), o (order), f (family), g (genus), or s
(species). The letter is followed by a colon (:) and the name of that rank. Commas and semicolons
are not allowed in the name of the rank.
Example:
">X80725_S000004313;tax=d:Bacteria,p:Proteobacteria,c:Gammaproteobacteria,o:Enterobacteriales,f:Enterobacteriaceae,g:Escherichia/Shigella,s:Escherichia_coli".
--db filename
Read the reference sequences from filename, in FASTA, FASTQ or UDB format. These
sequences needs to be annotated with taxonomy.
--sintax_cutoff real
Specify a minimum level of bootstrap support for the taxonomic ranks that will be
included in column 4 of the output file. For instance 0.9, corresponding to 90%.
--sintax filename
Read the input sequences from filename, in FASTA or FASTQ format.
--tabbedout filename
Write the results to filename, in a tab-separated text format. Column 1 contains the
query label. Column 2 contains the predicted taxonomy in the same format as for the

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reference data, with bootstrap support indicated in parentheses after each rank. Column
3 contains the strand. If the --sintax_cutoff option is used, the predicted taxonomy will
be repeated in column 4 while omitting the bootstrap values and including only the
ranks with support at or above the threshold.
UDB options:
Databases to be used with the --usearch_global command may be prepared from FASTA files and
stored to a binary UDB formatted file in order to speed up searching. This may be worthwhile
when searching a large database repeatedly. The sequences are indexed and stored in a way that
can be quickly loaded into memory. The commands and options below can be used to create and
inspect UDB files. An UDB file may be specified with the --db option instead of a FASTA formatted file with the --usearch_global command.
--dbmask none|dust|soft
Specify the sequence masking method used with the --makeudb_usearch command,
either none, dust or soft. No masking is performed when none is specified. When dust
is specified, the DUST algorithm will be used for masking low complexity regions
(short repeats and skewed composition). Lower case letters in the input file will be
masked when soft is specified (soft masking).
--hardmask
Mask sequences by replacing letters with N for the --makeudb_usearch command. The
default is to use lower case letters (soft masking).
--makeudb_usearch filename
Create an UDB database file from the FASTA-formatted sequences in the file with the
given filename. The UDB database is written to the file specified with the --output
option.
--output filename
Specify the filename of a FASTA or UDB output file for the --makeudb_usearch or the
--udb2fasta command, respectively.
--udb2fasta filename
Read the UDB database in the file with the given filename and output the sequences in
FASTA format in the file specified by the --output option.
--udbinfo filename
Show information about the UDB database in the file with the given filename.
--udbstats filename
Report statistics about the indexed words in the UDB database in the file with the given
filename.
--wordlength positive integer
Specify the length of the words to be used when creating the UDB database index
using the --makeudb_usearch command. Valid numbers range from 3 to 15. The default
is 8.
Userfields (fields accepted by the --userfields option):

version 2.10.4

aln

Print a string of M (match), D (delete, i.e. a gap in the query) and I (insert, i.e. a gap in
the target) representing the pairwise alignment. Empty field if there is no alignment.

alnlen

Print the length of the query-target alignment (number of columns). The field is set to 0
if there is no alignment.

bits

Bit score (not computed for nucleotide alignments). Always set to 0.

caln

Compact representation of the pairwise alignment using the CIGAR format (Compact
Idiosyncratic Gapped Alignment Report): M (match), D (deletion) and I (insertion).
Empty field if there is no alignment.

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vsearch(1)

evalue

E-value (not computed for nucleotide alignments). Always set to -1.

exts

Number of columns containing a gap extension (zero or positive integer value).

gaps

Number of columns containing a gap (zero or positive integer value).

Percentage of identity (real value ranging from 0.0 to 100.0). The percentage identity is
defined as 100 * (matching columns) / (alignment length - terminal gaps).

id0

CD-HIT definition of the percentage of identity (real value ranging from 0.0 to 100.0)
using the length of the shortest sequence in the pairwise alignment as denominator: 100
* (matching columns) / (shortest sequence length).

id1

The percentage of identity (real value ranging from 0.0 to 100.0) is defined as the edit
distance: 100 * (matching columns) / (alignment length).

id2

The percentage of identity (real value ranging from 0.0 to 100.0) is defined as the edit
distance, excluding terminal gaps. The field id2 is an alias for the field id.

id3

Marine Biological Lab definition of the percentage of identity (real value ranging from
0.0 to 100.0), counting each gap opening (internal or terminal) as a single mismatch,
whether or not the gap was extended, and using the length of the longest sequence in
the pairwise alignment as denominator: 100 * (1.0 - [(mismatches + gaps) / (longest
sequence length)]).

id4

BLAST definition of the percentage of identity (real value ranging from 0.0 to 100.0),
equivalent to --iddef 1 in a context of global pairwise alignment. The field id4 is always
equal to the field id1.

ids

Number of matches in the alignment (zero or positive integer value).

mism

Number of mismatches in the alignment (zero or positive integer value).

opens

Number of columns containing a gap opening (zero or positive integer value).

pairs

Number of columns containing only nucleotides. That value corresponds to the length
of the alignment minus the gap-containing columns (zero or positive integer value).

pctgaps

Number of columns containing gaps expressed as a percentage of the alignment length
(real value ranging from 0.0 to 100.0).

pctpv

Percentage of positive columns. When working with nucleotide sequences, this is
equivalent to the percentage of matches (real value ranging from 0.0 to 100.0).

Number of positive columns. When working with nucleotide sequences, this is equivalent to the number of matches (zero or positive integer value).

qcov

Fraction of the query sequence that is aligned with the target sequence (real value ranging from 0.0 to 100.0). The query coverage is computed as 100.0 * (matches + mismatches) / query sequence length. Internal or terminal gaps are not taken into account.
The field is set to 0.0 if there is no alignment.

qframe

Query frame (-3 to +3). That field only concerns coding sequences and is not computed
by vsearch. Always set to +0.

qhi

Last nucleotide of the query aligned with the target. Always equal to the length of the
pairwise alignment, 0 otherwise (see qihi to ignore terminal gaps).

qihi

Last nucleotide of the query aligned with the target (ignoring terminal gaps).
Nucleotide numbering starts from 1. The field is set to 0 if there is no alignment.

qilo

First nucleotide of the query aligned with the target (ignoring initial gaps). Nucleotide
numbering starts from 1. The field is set to 0 if there is no alignment.

Query sequence length (positive integer value). The field is set to 0 if there is no alignment.

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qlo

First nucleotide of the query aligned with the target. Always equal to 1 if there is an
alignment, 0 otherwise (see qilo to ignore initial gaps).

qrow

Print the sequence of the query segment as seen in the pairwise alignment (i.e. with gap
insertions if need be). Empty field if there is no alignment.

Query segment length. Always equal to query sequence length.

qstrand

Query strand orientation (+ or - for nucleotide sequences). Empty field if there is no
alignment.

query

Query label.

raw

Raw alignment score (negative, null or positive integer value). The score is the sum of
match rewards minus mismatch penalties, gap openings and gap extensions. The field
is set to 0 if there is no alignment.

target

Target label. The field is set to ’*’ if there is no alignment.

tcov

Fraction of the target sequence that is aligned with the query sequence (real value ranging from 0.0 to 100.0). The target coverage is computed as 100.0 * (matches + mismatches) / target sequence length. Internal or terminal gaps are not taken into account.
The field is set to 0.0 if there is no alignment.

tframe

Target frame (-3 to +3). That field only concerns coding sequences and is not computed
by vsearch. Always set to +0.

thi

Last nucleotide of the target aligned with the query. Always equal to the length of the
pairwise alignment, 0 otherwise (see tihi to ignore terminal gaps).

tihi

Last nucleotide of the target aligned with the query (ignoring terminal gaps).
Nucleotide numbering starts from 1. The field is set to 0 if there is no alignment.

tilo

First nucleotide of the target aligned with the query (ignoring initial gaps). Nucleotide
numbering starts from 1. The field is set to 0 if there is no alignment.

Target sequence length (positive integer value). The field is set to 0 if there is no alignment.

tlo

First nucleotide of the target aligned with the query. Always equal to 1 if there is an
alignment, 0 otherwise (see tilo to ignore initial gaps).

trow

Print the sequence of the target segment as seen in the pairwise alignment (i.e. with gap
insertions if need be). Empty field if there is no alignment.

Target segment length. Always equal to target sequence length. The field is set to 0 if
there is no alignment.

tstrand

Target strand orientation (+ or - for nucleotide sequences). Always set to ’+’, so reverse
strand matches have tstrand ’+’ and qstrand

DELIBERATE CHANGES
If you are a usearch user, our objective is to make you feel at home. That’s why vsearch was designed to
behave like usearch, to some extent. Like any complex software, usearch is not free from quirks and inconsistencies. We decided not to reproduce some of them, and for complete transparency, to document here the
deliberate changes we made.
During a search with usearch, when using the options --blast6out and --output_no_hits, for queries with no
match the number of fields reported is 13, where it should be 12. This is corrected in vsearch.
The field raw of the --userfields option is not informative in usearch. This is corrected in vsearch.
The fields qlo, qhi, tlo, thi now have counterparts (qilo, qihi, tilo, tihi) reporting alignment coordinates
ignoring terminal gaps.
In usearch, when using the option --output_no_hits, queries that receive no match are reported in
--blast6out file, but not in the alignment output file. This is corrected in vsearch.

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vsearch introduces a new --cluster_size command that sorts sequences by decreasing abundance before
clustering.
vsearch reintroduces --iddef alternative pairwise identity definitions that were removed from usearch.
vsearch extends the --topn option to sorting commands.
vsearch extends the --sizein option to dereplication (--derep_fulllength) and clustering (--cluster_fast).
vsearch treats T and U as identical nucleotides during dereplication.
vsearch sorting is stabilized by using sequence abundances or sequences labels as secondary or tertiary
keys.
vsearch by default uses the DUST algorithm for masking low-complexity regions. Masking behavior is
also slightly changed to be more consistent.

NOVELTIES
vsearch introduces new commands and new options not present in usearch 7. They are described in the
’Options’ section of this manual. Here is a short list:
- uchime2_denovo, uchime3_denovo, alignwidth, borderline, fasta_score (chimera checking)
- cluster_size, cluster_unoise, clusterout_id, clusterout_sort, profile (clustering)
- fasta_width, gzip_decompress, bzip2_decompress (general option)
- iddef (clustering, pairwise alignment, searching)
- maxuniquesize (dereplication)
- relabel_md5 and relabel_sha1 (chimera detection, dereplication, FASTQ processing, shuffling,
sorting)
- shuffle (shuffling)
- fastq_eestats, fastq_eestats2, fastq_maxlen, fastq_truncee (FASTQ processing)
- fastaout_discarded, fastqout_discarded (subsampling)
- rereplicate (dereplication/rereplication)

EXAMPLES
Align all sequences in a database with each other and output all pairwise alignments:
vsearch --allpairs_global database.fas --alnout results.aln --acceptall
Check for the presence of chimeras (de novo); parents should be at least 1.5 times more abundant than
chimeras. Output non-chimeric sequences in fasta format (no wrapping):
vsearch --uchime_denovo queries.fas --abskew 1.5 --nonchimeras results.fas --fasta_width 0
Cluster with a 97% similarity threshold, collect cluster centroids, and write cluster descriptions using a
uclust-like format:
vsearch --cluster_fast queries.fas --id 0.97 --centroids centroids.fas --uc clusters.uc
Dereplicate the sequences contained in queries.fas, take into account the abundance information already
present, write unwrapped fasta sequences to queries_unique.fas with the new abundance information, discard all sequences with an abundance of 1:
vsearch --derep_fulllength queries.fas
queries_unique.fas --minuniquesize 2

--sizein

--fasta_width

--sizeout

--output

Mask simple repeats and low complexity regions in the input fasta file with the DUST algorithm (masked
regions are lowercased), and write the results to the output file:
vsearch --maskfasta queries.fas --qmask dust --output queries_masked.fas
Search queries in a reference database, with a 80%-similarity threshold, take terminal gaps into account

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when calculating pairwise similarities, output pairwise alignments:
vsearch --usearch_global queries.fas --db references.fas --id 0.8 --iddef 1 --alnout results.aln
Search a sequence dataset against itself (ignore self hits), get all matches with at least 60% similarity, and
collect results in a blast-like tab-separated format. Accept an unlimited number of hits (--maxaccepts 0),
and compare each query to all other sequences, including unlikely candidates (--maxrejects 0):
vsearch --usearch_global queries.fas --db queries.fas --self --id 0.6 --blast6out results.blast6
--maxaccepts 0 --maxrejects 0
Shuffle the input fasta file (change the order of sequences) in a repeatable fashion (fixed seed), and write
unwrapped fasta sequences to the output file:
vsearch --shuffle queries.fas --output queries_shuffled.fas --randseed 13 --fasta_width 0
Sort by decreasing abundance the sequences contained in queries.fas (using the ’size=integer’ information),
relabel the sequences while preserving the abundance information (with --sizeout), keep only sequences
with an abundance equal to or greater than 2:
vsearch --sortbysize queries.fas --output queries_sorted.fas --relabel sampleA_ --sizeout --minsize 2

AUTHORS
Implementation by Torbjørn Rognes and Tomás Flouri, documentation by Frédéric Mahé.

CITATION
Rognes T, Flouri T, Nichols B, Quince C, Mahé F. (2016) VSEARCH: a versatile open source tool for
metagenomics. PeerJ 4:e2584 doi: 10.7717/peerj.2584

REPORTING BUGS
Submit suggestions and bug-reports at , send a pull request on
, or compose a friendly or curmudgeont e-mail to Torbjørn Rognes
.

AVAILABILITY
Source code and binaries are available at .

COPYRIGHT
Copyright (C) 2014-2018, Torbjørn Rognes, Frédéric Mahé and Tomás Flouri
All rights reserved.
Contact: Torbjørn Rognes , Department of Informatics, University of Oslo, PO Box
1080 Blindern, NO-0316 Oslo, Norway
This software is dual-licensed and available under a choice of one of two licenses, either under the terms of
the GNU General Public License version 3 or the BSD 2-Clause License.
GNU General Public License version 3
This program is free software: you can redistribute it and/or modify it under the terms of the GNU General
Public License as published by the Free Software Foundation, either version 3 of the License, or (at your
option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without
even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program. If not, see
.
The BSD 2-Clause License
Redistribution and use in source and binary forms, with or without modification, are permitted provided

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vsearch(1)

that the following conditions are met:
1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the
following disclaimer in the documentation and/or other materials provided with the distribution.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
We would like to thank the authors of the following projects for making their source code available:
- vsearch includes code from Google’s CityHash project by Geoff Pike and Jyrki Alakuijala, providing some excellent hash functions available under a MIT license.
- vsearch includes code derived from Tatusov and Lipman’s DUST program that is in the public
domain.
- vsearch includes public domain code written by Alexander Peslyak for the MD5 message digest
algorithm.
- vsearch includes public domain code written by Steve Reid and others for the SHA1 message
digest algorithm.
- vsearch binaries may include code from the zlib library, copyright Jean-Loup Gailly and Mark
Adler.
- vsearch binaries may include code from the bzip2 library, copyright Julian R. Seward.

SEE ALSO
swipe, an extremely fast pairwise local (Smith-Waterman) database search tool by Torbjørn Rognes, available at .
swarm, a fast and accurate amplicon clustering method by Frédéric Mahé and Torbjørn Rognes, available
at .

VERSION HISTORY
New features and important modifications of vsearch (short lived or minor bug releases may not be mentioned):
v1.0.0 released November 28th, 2014
First public release.
v1.0.1 released December 1st, 2014
Bug fixes (sortbysize, semicolon after size annotation in headers) and minor changes
(labels as secondary sort key for most sorts, treat T and U as identical for dereplication,
only output size in --dbmatched file if --sizeout specified).
v1.0.2 released December 6th, 2014
Bug fixes (ssse3/sse4.1 requirement, memory leak).
v1.0.3 released December 6th, 2014
Bug fix (now writes help to stdout instead of stderr).

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vsearch(1)

v1.0.4 released December 8th, 2014
Added --allpairs_global option. Reduce memory requirements slightly and eliminate
memory leaks.
v1.0.5 released December 9th, 2014
Fixes a minor bug with --allpairs_global and --acceptall options.
v1.0.6 released December 14th, 2014
Fixes a memory allocation bug in chimera detection (--uchime_ref option).
v1.0.7 released December 19th, 2014
Fixes a bug in the output from chimera detection with the --uchimeout option.
v1.0.8 released January 22nd, 2015
Introduces several changes and bug fixes:
- a new linear memory aligner for alignment of sequences longer than 5,000 nucleotides,
- a new --cluster_size command that sorts sequences by decreasing abundance before
clustering,
- meaning of userfields qlo, qhi, tlo, thi changed for compatibility with usearch,
- new userfields qilo, qihi, tilo, tihi give alignment coordinates ignoring terminal gaps,
- in --uc output files, a perfect alignment is indicated with a ’=’ sign,
- the option --cluster_fast now sorts sequences by decreasing length, then by decreasing
abundance and finally by sequence identifier,
- default --maxseqlength value set to 50,000 nucleotides,
- fix for bug in alignment in rare cases,
- fix for lack of detection of under- or overflow in SIMD aligner.
v1.0.9 released January 22nd, 2015
Fixes a bug in the function sorting sequences by decreasing abundance (--sortbysize).
v1.0.10 released January 23rd, 2015
Fixes a bug where the --sizein option was ignored and always treated as on, affecting
clustering and dereplication commands.
v1.0.11 released February 5th, 2015
Introduces the possibility to output results in SAM format (for clustering, pairwise alignment and searching).
v1.0.12 released February 6th, 2015
Temporarily fixes a problem with long headers in FASTA files.
v1.0.13 released February 17th, 2015
Fix a memory allocation problem when computing multiple sequence alignments with the
--msaout and --consout options, as well as a memory leak. Also increased line buffer for
reading FASTA files to 4MB.
v1.0.14 released February 17th, 2015
Fix a bug where the multiple alignment and consensus sequence computed after clustering ignored the strand of the sequences. Also decreased size of line buffer for reading
FASTA files to 1MB again due to excessive stack memory usage.
v1.0.15 released February 18th, 2015
Fix bug in calculation of identity metric between sequences when using the MBL definition (--iddef 3).
v1.0.16 released February 19th, 2015
Integrated patches from Debian for increased compatibility with various architectures.

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v1.1.0 released February 20th, 2015
Added the --quiet option to suppress all output to stdout and stderr except for warnings
and fatal errors. Added the --log option to write messages to a log file.
v1.1.1 released February 20th, 2015
Added info about --log and --quiet options to help text.
v1.1.2 released March 18th, 2015
Fix bug with large datasets. Fix format of help info.
v1.1.3 released March 18th, 2015
Fix more bugs with large datasets.
v1.2.0-1.2.19 released July 6th to September 8th, 2015
Several new commands and options added. Bugs fixed. Documentation updated.
v1.3.0 released September 9th, 2015
Changed to autotools build system.
v1.3.1 released September 14th, 2015
Several new commands and options. Bug fixes.
v1.3.2 released September 15th, 2015
Fixed memory leaks. Added ’-h’ shortcut for help. Removed extra ’v’ in version number.
v1.3.3 released September 15th, 2015
Fixed bug in hexadecimal digits of MD5 and SHA1 digests. Added --samheader option.
v1.3.4 released September 16th, 2015
Fixed compilation problems with zlib and bzip2lib.
v1.3.5 released September 17th, 2015
Minor configuration/makefile changes to compile to native CPU and simplify makefile.
v1.4.0 released September 25th, 2015
Added --sizeorder option.
v1.4.1 released September 29th, 2015
Inserted public domain MD5 and SHA1 code to eliminate dependency on crypto and
openssl libraries and their licensing issues.
v1.4.2 released October 2nd, 2015
Dynamic loading of libraries for reading gzip and bzip2 compressed files if available. Circumvention of missing gzoffset function in zlib 1.2.3 and earlier.
v1.4.3 released October 3rd, 2015
Fix a bug with determining amount of memory on some versions of Apple OS X.
v1.4.4 released October 3rd, 2015
Remove debug message.
v1.4.5 released October 6th, 2015
Fix memory allocation bug when reading long FASTA sequences.
v1.4.6 released October 6th, 2015
Fix subtle bug in SIMD alignment code that reduced accuracy.
v1.4.7 released October 7th, 2015
Fixes a problem with searching for or clustering sequences with repeats. In this new version, vsearch looks at all words occurring at least once in the sequences in the initial step.
Previously only words occurring exactly once were considered. In addition, vsearch now
requires at least 10 words to be shared by the sequences, previously only 6 were required.
If the query contains less than 10 words, all words must be present for a match. This
change seems to lead to slightly reduced recall, but somewhat increased precision, ending
up with slightly improved overall accuracy.

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v1.5.0 released October 7th, 2015
This version introduces the new option --minwordmatches that allows the user to specify
the minimum number of matching unique words before a sequence is considered further.
New default values for different word lengths are also set. The minimum word length is
increased to 7.
v1.6.0 released October 9th, 2015
This version adds the relabeling options (--relabel, --relabel_md5 and --relabel_sha1) to
the shuffle command. It also adds the --xsize option to the clustering, dereplication, shuffling and sorting commands.
v1.6.1 released October 14th, 2015
Fix bugs and update manual and help text regarding relabelling. Add all relabelling
options to the subsampling command. Add the --xsize option to chimera detection,
dereplication and fastq filtering commands. Refactoring of code.
v1.7.0 released October 14th, 2015
Add --relabel_keep option.
v1.8.0 released October 19th, 2015
Added --search_exact, --fastx_mask and --fastq_convert commands. Changed most commands to read FASTQ input files as well as FASTA files. Modified --fastx_revcomp and
--fastx_subsample to write FASTQ files.
v1.8.1 released November 2nd, 2015
Fixes for compatibility with QIIME and older OS X versions.
v1.9.0 released November 12th, 2015
Added the --fastq_mergepairs command and associated options. This command has not
been tested well yet. Included additional files to avoid dependency of autoconf for compilation. Fixed an error where identifiers in fasta headers where not truncated at tabs, just
spaces. Fixed a bug in detection of the file format (FASTA/FASTQ) of a gzip compressed
input file.
v1.9.1 released November 13th, 2015
Fixed memory leak and a bug in score computation in --fastq_mergepairs, and improved
speed.
v1.9.2 released November 17th, 2015
Fixed a bug in the computation of some values with --fastq_stats.
v1.9.3 released November 19th, 2015
Workaround for missing x86intrin.h with old compilers.
v1.9.4 released December 3rd, 2015
Fixed incrementation of counter when relabeling dereplicated sequences.
v1.9.5 released December 3rd, 2015
Fixed bug resulting in inferior chimera detection performance.
v1.9.6 released January 8th, 2016
Fixed bug in aligned sequences produced with --fastapairs and --userout (qrow, trow)
options.
v1.9.7 released January 12th, 2016
Masking behavior is changed somewhat to keep the letter case of the input sequences
unchanged when no masking is performed. Masking is now performed also during
chimera detection. Documentation updated.
v1.9.8 released January 22nd, 2016
Fixed bug causing segfault when chimera detection is performed on extremely short
sequences.

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v1.9.9 released January 22nd, 2016
Adjusted default minimum number of word matches during searches for improved performance.
v1.9.10 released January 25th, 2016
Fixed bug related to masking and lower case database sequences.
v1.10.0 released February 11th, 2016
Parallelized and improved merging of paired-end reads and adjusted some defaults.
Removed progress indicator when stderr is not a terminal. Added --fasta_score option to
report chimera scores in FASTA files. Added --rereplicate and --fastq_eestats commands.
Fixed typos. Added relabelling to files produced with --consout and --profile options.
v1.10.1 released February 23rd, 2016
Fixed a bug affecting the --fastq_mergepairs command causing FASTQ headers to be
truncated at first space (despite the bug fix release 1.9.0 of November 12th, 2015). Full
headers are now included in the output (no matter if --notrunclabels is in effect or not).
v1.10.2 released March 18th, 2016
Fixed a bug causing a segmentation fault when running --usearch_global with an empty
query sequence. Also fixed a bug causing imperfect alignments to be reported with an
alignment string of ’=’ in uc output files. Fixed typos in man file. Fixed fasta/fastq processing code regarding presence or absence of compression library header files.
v1.11.1 released April 13th, 2016
Added strand information in UC file for --derep_fulllength and --derep_prefix. Added
expected errors (ee) to header of FASTA files specified with --fastaout and --fastaout_discarded when --eeout or --fastq_eeout option is in effect for fastq_filter and fastq_mergepairs. The options --eeout and --fastq_eeout are now equivalent.
v1.11.2 released June 21st, 2016
Two bugs were fixed. The first issue was related to the --query_cov option that used a different coverage definition than the qcov userfield. The coverage is now defined as the
fraction of the whole query sequence length that is aligned with matching or mismatching
residues in the target. All gaps are ignored. The other issue was related to the consensus
sequences produced during clustering when only N’s were present in some positions. Previously these would be converted to A’s in the consensus. The behaviour is changed so
that N’s are produced in the consensus, and it should now be more compatible with usearch.
v2.0.0 released June 24th, 2016
This major new version supports reading from pipes. Two new options are added:
--gzip_decompress and --bzip2_decompress. One of these options must be specified if
reading compressed input from a pipe, but are not required when reading from ordinary
files. The vsearch header that was previously written to stdout is now written to stderr.
This enables piping of results for further processing. The file name ’-’ now represent standard input (/dev/stdin) or standard output (/dev/stdout) when reading or writing files,
respectively. Code for reading FASTA and FASTQ files has been refactored.
v2.0.1 released June 30th, 2016
Avoid segmentation fault when masking very long sequences.
v2.0.2 released July 5th, 2016
Avoid warnings when compiling with GCC 6.
v2.0.3 released August 2nd, 2016
Fixed bad compiler options resulting in Illegal instruction errors when running precompiled binaries.

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v2.0.4 released September 1st, 2016
Improved error message for bad FASTQ quality values. Improved manual.
v2.0.5 released September 9th, 2016
Add options --fastaout_discarded and --fastqout_discarded to output discarded sequences
from subsampling to separate files. Updated manual.
v2.1.0 released September 16th, 2016
New command: --fastx_filter. New options: --fastq_maxlen, --fastq_truncee. Allow --minwordmatches down to 3.
v2.1.1 released September 23rd, 2016
Fixed bugs in output to UC-files. Improved help text and manual.
v2.1.2 released September 28th, 2016
Fixed incorrect abundance output from fastx_filter and fastq_filter when relabelling.
v2.2.0 released October 7th, 2016
Added OTU table generation options --biomout, --mothur_shared_out and --otutabout to
the clustering and searching commands.
v2.3.0 released October 10th, 2016
Allowed zero-length sequences in FASTA and FASTQ files. Added --fastq_trunclen_keep
option. Fixed bug with output of OTU tables to pipes.
v2.3.1 released November 16th, 2016
Fixed bug where --minwordmatches 0 was interpreted as the default minimum word
matches for the given word length instead of zero. When used in combination with
--maxaccepts 0 and --maxrejects 0 it will allow complete bypass of kmer-based heuristics.
v2.3.2 released November 18th, 2016
Fixed bug where vsearch reported the ordinal number of the target sequence instead of
the cluster number in column 2 on H-lines in the uc output file after clustering. For search
and alignment commands both usearch and vsearch reports the target sequence number
here.
v2.3.3 released December 5th, 2016
A minor speed improvement.
v2.3.4 released December 9th, 2016
Fixed bug in output of sequence profiles and updated documentation.
v2.4.0 released February 8th, 2017
Added support for Linux on Power8 systems (ppc64le) and Windows on x86_64.
Improved detection of pipes when reading FASTA and FASTQ files. Corrected option for
specifiying output from fastq_eestats command in help text.
v2.4.1 released March 1st, 2017
Fixed an overflow bug in fastq_stats and fastq_eestats affecting analysis of very large
FASTQ files. Fixed maximum memory usage reporting on Windows.
v2.4.2 released March 10th, 2017
Default value for fastq_minovlen increased to 16 in accordance with help text and for
compatibility with usearch. Minor changes for improved accuracy of paired-end read
merging.
v2.4.3 released April 6th, 2017
Fixed bug with progress bar for shuffling. Fixed missing N-lines in UC files with usearch_global, search_exact and allpairs_global when the output_no_hits option was not
specified.

version 2.10.4

January 4, 2019

vsearch(1)

USER COMMANDS

vsearch(1)

v2.4.4 released August 28th, 2017
Fixed a few minor bugs, improved error messages and updated documentation.
v2.5.0 released October 5th, 2017
Support for UDB database files. New commands: fastq_stripright, fastq_eestats2,
makeudb_usearch, udb2fasta, udbinfo, and udbstats. New general option: no_progress.
New options minsize and maxsize to fastx_filter. Minor bug fixes, error message
improvements and documentation updates.
v2.5.1 released October 25th, 2017
Fixed bug with bad default value of 1 instead of 32 for minseqlength when using the
makeudb_usearch command.
v2.5.2 released October 30th, 2017
Fixed bug with where ’-’ as an argument to the fastq_eestats2 option was treated literally
instead of equivalent to stdin.
v2.6.0 released November 10th, 2017
Rewritten paired-end reads merger with improved accuracy. Decreased default value for
fastq_minovlen option from 16 to 10. The default value for the fastq_maxdiffs option is
increased from 5 to 10. There are now other more important restrictions that will avoid
merging reads that cannot be reliably aligned.
v2.6.1 released December 8th, 2017
Improved parallelisation of paired end reads merging.
v2.6.2 released December 18th, 2017
Fixed option xsize that was partially inactive for commands uchime_denovo, uchime_ref,
and fastx_filter.
v2.7.0 released February 13th, 2018
Added commands cluster_unoise, uchime2_denovo and uchime3_denovo contributed by
Davide Albanese based on Robert Edgar’s papers. Refactored fasta and fastq print functions as well as code for extraction of abundance and other attributes from the headers.
v2.7.1 released February 16th, 2018
Fix several bugs on Windows related to large files, use of "-" as a file name to mean stdin
or stdout, alignment errors, missed kmers and corrupted UDB files. Added documentation
of UDB-related commands.
v2.7.2 released April 20th, 2018
Added the sintax command for taxonomic classification. Fixed a bug with incorrect
FASTA headers of consensus sequences after clustering.
v2.8.0 released April 24th, 2018
Added the fastq_maxdiffpct option to the fastq_mergepairs command.
v2.8.1 released June 22nd, 2018
Fixes for compilation warnings with GCC 8.
v2.8.2 released August 21st, 2018
Fix for wrong placement of semicolons in header lines in some cases when using the
sizeout or xsize options. Reduced memory requirements for full-length dereplication in
cases with many duplicate sequences. Improved wording of fastq_mergepairs report.
Updated manual regarding use of sizein and sizeout with dereplication. Changed a compiler option.
v2.8.3 released August 31st, 2018
Fix for segmentation fault for --derep_fulllength with --uc.
v2.8.4 released September 3rd, 2018
Further reduce memory requirements for dereplication when not using the uc option. Fix
output during subsampling when quiet or log options are in effect.

version 2.10.4

January 4, 2019

vsearch(1)

USER COMMANDS

vsearch(1)

v2.8.5 released September 26th, 2018
Fixed a bug in fastq_eestats2 that caused the values for large lengths to be much too high
when the input sequences had varying lengths.
v2.8.6 released October 9th, 2018
Fixed a bug introduced in version 2.8.2 that caused derep_fulllength to include the full
FASTA header in its output instead of stopping at the first space (unless the notrunclabels
option is in effect).
v2.9.0 released October 10th, 2018
Added the fastq_join command.
v2.9.1 released October 29th, 2018
Changed compiler options that select the target cpu and tuning to allow the software to
run on any 64-bit x86 system, while tuning for more modern variants. Avoid illegal
instruction error on some architectures. Update documentation of rereplicate command.
v2.10.0 released December 6th, 2018
Added the sff_convert commmand to convert SFF files to FASTQ. Added some additional option argument checks. Fixed segmentation fault bug after some fatal errors when
a log file was specified.
v2.10.1 released December 7th, 2018
Improved sff_convert command. It will now read several variants of the SFF format. It is
also able to read from a pipe. Warnings are given if there are minor problems. Errors messages have been improved. Minor speed and memory usage improvements.
v2.10.2 released December 10th, 2018
Fixed bug in sintax with reversed order of domain and kingdom.
v2.10.3 released December 19th, 2018
Ported to Linux on ARMv8 (aarch64). Fixed compilation warning with gcc version 8.1.0
and 8.2.0.
v2.10.4 released January 4th, 2019
Fixed serious bug in x86_64 SIMD alignment code introduced in version 2.10.3. Added
link to BioConda in README. Fixed bug in fastq_stats with sequence length 1. Fixed
use of equals symbol in UC files for identical sequences with cluster_fast.

version 2.10.4

January 4, 2019

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