Provided by: trim-galore_0.6.10-1_all 
NAME
trim_galore - automate quality and adapter trimming for DNA sequencing
DESCRIPTION
USAGE:
trim_galore [options] <filename(s)>
-h/--help Print this help message and exits.
-v/--version Print the version information and exits.
-q/--quality <INT> Trim low-quality ends from reads in addition to adapter removal. For
RRBS samples, quality trimming will be performed first, and adapter
trimming is carried in a second round. Other files are quality and adapter trimmed in a single
pass. The algorithm is the same as the one used by BWA (Subtract INT from all qualities; compute
partial sums from all indices to the end of the sequence; cut sequence at the index at which the
sum is minimal). Default Phred score: 20.
--phred33 Instructs Cutadapt to use ASCII+33 quality scores as Phred scores
(Sanger/Illumina 1.9+ encoding) for quality trimming. Default: ON.
--phred64 Instructs Cutadapt to use ASCII+64 quality scores as Phred scores
(Illumina 1.5 encoding) for quality trimming.
--fastqc Run FastQC in the default mode on the FastQ file once trimming is complete.
--fastqc_args "<ARGS>" Passes extra arguments to FastQC. If more than one argument is to be passed
to FastQC they must be in the form "arg1 arg2 etc.". An example would be:
--fastqc_args "--nogroup --outdir /home/". Passing extra arguments will automatically invoke
FastQC, so --fastqc does not have to be specified separately.
-a/--adapter <STRING> Adapter sequence to be trimmed. If not specified explicitly, Trim Galore will
try to auto-detect whether the Illumina universal, Nextera transposase or Illumina
small RNA adapter sequence was used. Also see '--illumina', '--nextera' and '--small_rna'. If no
adapter can be detected within the first 1 million sequences of the first file specified or if
there is a tie between several adapter sequences, Trim Galore defaults to '--illumina' (as long as
the Illumina adapter was one of the options, else '--nextera' is the default). A single base may
also be given as e.g. -a A{10}, to be expanded to -a AAAAAAAAAA.
-a2/--adapter2 <STRING> Optional adapter sequence to be trimmed off read 2 of paired-end files. This
option requires '--paired' to be specified as well. If the libraries to be trimmed
are smallRNA then a2 will be set to the Illumina small RNA 5' adapter automatically
(GATCGTCGGACT). A single base may also be given as e.g. -a2 A{10}, to be expanded to -a2
AAAAAAAAAA.
--illumina Adapter sequence to be trimmed is the first 13bp of the Illumina universal
adapter
'AGATCGGAAGAGC' instead of the default auto-detection of adapter sequence.
--nextera Adapter sequence to be trimmed is the first 12bp of the Nextera adapter
'CTGTCTCTTATA' instead of the default auto-detection of adapter sequence.
--small_rna Adapter sequence to be trimmed is the first 12bp of the Illumina Small RNA 3'
Adapter
'TGGAATTCTCGG' instead of the default auto-detection of adapter sequence. Selecting
to trim smallRNA adapters will also lower the --length value to 18bp. If the smallRNA libraries
are paired-end then a2 will be set to the Illumina small RNA 5' adapter automatically
(GATCGTCGGACT) unless -a 2 had been defined explicitly.
--consider_already_trimmed <INT> During adapter auto-detection, the limit set by <INT> allows the
user to
set a threshold up to which the file is considered already adapter-trimmed. If no adapter
sequence exceeds this threshold, no additional adapter trimming will be performed (technically,
the adapter is set to '-a X'). Quality trimming is still performed as usual. Default: NOT
SELECTED (i.e. normal auto-detection precedence rules apply).
--max_length <INT> Discard reads that are longer than <INT> bp after trimming. This is only advised
for
smallRNA sequencing to remove non-small RNA sequences.
--stringency <INT> Overlap with adapter sequence required to trim a sequence. Defaults to a
very stringent setting of 1, i.e. even a single bp of overlapping sequence
will be trimmed off from the 3' end of any read.
-e <ERROR RATE> Maximum allowed error rate (no. of errors divided by the length of the matching
region) (default: 0.1)
--gzip Compress the output file with GZIP. If the input files are GZIP-compressed
the output files will automatically be GZIP compressed as well. As of v0.2.8 the
compression will take place on the fly.
--dont_gzip Output files won't be compressed with GZIP. This option overrides --gzip.
--length <INT> Discard reads that became shorter than length INT because of either
quality or adapter trimming. A value of '0' effectively disables
this behaviour. Default: 20 bp.
For paired-end files, both reads of a read-pair need to be longer than
<INT> bp to be printed out to validated paired-end files (see option --paired). If only one read
became too short there is the possibility of keeping such unpaired single-end reads (see
--retain_unpaired). Default pair-cutoff: 20 bp.
--max_n COUNT The total number of Ns (as integer) a read may contain before it will be removed
altogether.
In a paired-end setting, either read exceeding this limit will result in the entire
pair being removed from the trimmed output files.
--trim-n Removes Ns from either side of the read. This option does currently not work in
RRBS mode.
-o/--output_dir <DIR> If specified all output will be written to this directory instead of the current
directory. If the directory doesn't exist it will be created for you.
--no_report_file If specified no report file will be generated.
--suppress_warn If specified any output to STDOUT or STDERR will be suppressed.
--clip_R1 <int> Instructs Trim Galore to remove <int> bp from the 5' end of read 1 (or single-end
reads). This may be useful if the qualities were very poor, or if there is some
sort of unwanted bias at the 5' end. Default: OFF.
--clip_R2 <int> Instructs Trim Galore to remove <int> bp from the 5' end of read 2 (paired-end
reads
only). This may be useful if the qualities were very poor, or if there is some sort
of unwanted bias at the 5' end. For paired-end BS-Seq, it is recommended to remove the first few
bp because the end-repair reaction may introduce a bias towards low methylation. Please refer to
the M-bias plot section in the Bismark User Guide for some examples. Default: OFF.
--three_prime_clip_R1 <int> Instructs Trim Galore to remove <int> bp from the 3' end of read 1 (or
single-end
reads) AFTER adapter/quality trimming has been performed. This may remove some unwanted
bias from the 3' end that is not directly related to adapter sequence or basecall quality.
Default: OFF.
--three_prime_clip_R2 <int> Instructs Trim Galore to remove <int> bp from the 3' end of read 2 AFTER
adapter/quality trimming has been performed. This may remove some unwanted bias from
the 3' end that is not directly related to adapter sequence or basecall quality. Default: OFF.
--2colour/--nextseq INT This enables the option '--nextseq-trim=3'CUTOFF' within Cutadapt, which will set
a quality
cutoff (that is normally given with -q instead), but qualities of G bases are ignored.
This trimming is in common for the NextSeq- and NovaSeq-platforms, where basecalls without any
signal are called as high-quality G bases. This is mutually exlusive with '-q INT'.
--path_to_cutadapt </path/to/cutadapt> You may use this option to specify a path to the Cutadapt
executable,
e.g. /my/home/cutadapt-1.7.1/bin/cutadapt. Else it is assumed that Cutadapt is in
the PATH.
--basename <PREFERRED_NAME> Use PREFERRED_NAME as the basename for output files, instead of deriving
the filenames from
the input files. Single-end data would be called PREFERRED_NAME_trimmed.fq(.gz), or
PREFERRED_NAME_val_1.fq(.gz) and PREFERRED_NAME_val_2.fq(.gz) for paired-end data. --basename only
works when 1 file (single-end) or 2 files (paired-end) are specified, but not for longer lists.
-j/--cores INT Number of cores to be used for trimming [default: 1]. For Cutadapt to work with
multiple cores, it
requires Python 3 as well as parallel gzip (pigz) installed on the system. The version of Python used
is detected from the shebang line of the Cutadapt executable (either 'cutadapt', or a specified
path). If Python 2 is detected, --cores is set to 1. If pigz cannot be detected on your system,
Trim Galore reverts to using gzip compression. Please note that gzip compression will slow down
multi-core processes so much that it is hardly worthwhile, please see:
https://github.com/FelixKrueger/TrimGalore/issues/16#issuecomment-458557103 for more info).
Actual core usage: It should be mentioned that the actual number of cores used is a little convoluted.
Assuming that Python 3 is used and pigz is installed, --cores 2 would use 2 cores to read the
input (probably not at a high usage though), 2 cores to write to the output (at moderately high
usage), and 2 cores for Cutadapt itself + 2 additional cores for Cutadapt (not sure what they are
used for) + 1 core for Trim Galore itself. So this can be up to 9 cores, even though most of them
won't be used at 100% for most of the time. Paired-end processing uses twice as many cores for the
validation (= writing out) step. --cores 4 would then be: 4 (read) + 4 (write) + 4 (Cutadapt) + 2
(extra Cutadapt) + 1 (Trim Galore) = 15.
It seems that --cores 4 could be a sweet spot, anything above has diminishing returns.
SPECIFIC TRIMMING - without adapter/quality trimming
--hardtrim5 <int> Instead of performing adapter-/quality trimming, this option will simply
hard-trim sequences
to <int> bp at the 5'-end. Once hard-trimming of files is complete, Trim Galore will exit.
Hard-trimmed output files will end in .<int>_5prime.fq(.gz). Here is an example:
before:
CCTAAGGAAACAAGTACACTCCACACATGCATAAAGGAAATCAAATGTTATTTTTAAGAAAATGGAAAAT
--hardtrim5 20: CCTAAGGAAACAAGTACACT
--hardtrim3 <int> Instead of performing adapter-/quality trimming, this option will simply
hard-trim sequences
to <int> bp at the 3'-end. Once hard-trimming of files is complete, Trim Galore will exit.
Hard-trimmed output files will end in .<int>_3prime.fq(.gz). Here is an example:
before:
CCTAAGGAAACAAGTACACTCCACACATGCATAAAGGAAATCAAATGTTATTTTTAAGAAAATGGAAAAT
--hardtrim3 20:
TTTTTAAGAAAATGGAAAAT
--clock In this mode, reads are trimmed in a specific way that is currently used for the
Mouse
Epigenetic Clock (see here: Multi-tissue DNA methylation age predictor in mouse, Stubbs et al.,
Genome Biology, 2017 18:68 https://doi.org/10.1186/s13059-017-1203-5). Following this, Trim Galore
will exit.
In it's current implementation, the dual-UMI RRBS reads come in the following format:
Read 1 5' UUUUUUUU CAGTA FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF TACTG UUUUUUUU 3'
Read 2 3' UUUUUUUU GTCAT FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF ATGAC UUUUUUUU 5'
Where UUUUUUUU is a random 8-mer unique molecular identifier (UMI), CAGTA is a constant region,
and FFFFFFF... is the actual RRBS-Fragment to be sequenced. The UMIs for Read 1 (R1) and Read 2
(R2), as well as the fixed sequences (F1 or F2), are written into the read ID and removed from the
actual sequence. Here is an example:
R1: @HWI-D00436:407:CCAETANXX:1:1101:4105:1905 1:N:0: CGATGTTT
ATCTAGTTCAGTACGGTGTTTTCGAATTAGAAAAATATGTATAGAGGAAATAGATATAAAGGCGTATTCGTTATTG
R2: @HWI-D00436:407:CCAETANXX:1:1101:4105:1905 3:N:0: CGATGTTT
CAATTTTGCAGTACAAAAATAATACCTCCTCTATTTATCCAAAATCACAAAAAACCACCCACTTAACTTTCCCTAA
R1: @HWI-D00436:407:CCAETANXX:1:1101:4105:1905 1:N:0: CGATGTTT:R1:ATCTAGTT:R2:CAATTTTG:F1:CAGT:F2:CAGT
CGGTGTTTTCGAATTAGAAAAATATGTATAGAGGAAATAGATATAAAGGCGTATTCGTTATTG
R2: @HWI-D00436:407:CCAETANXX:1:1101:4105:1905 3:N:0: CGATGTTT:R1:ATCTAGTT:R2:CAATTTTG:F1:CAGT:F2:CAGT
CAAAAATAATACCTCCTCTATTTATCCAAAATCACAAAAAACCACCCACTTAACTTTCCCTAA
Following clock trimming, the resulting files (.clock_UMI.R1.fq(.gz) and .clock_UMI.R2.fq(.gz))
should be adapter- and quality trimmed with Trim Galore as usual. In addition, reads need to be
trimmed by 15bp from their 3' end to get rid of potential UMI and fixed sequences. The command is:
trim_galore --paired --three_prime_clip_R1 15 --three_prime_clip_R2 15 *.clock_UMI.R1.fq.gz
*.clock_UMI.R2.fq.gz
Following this, reads should be aligned with Bismark and deduplicated with UmiBam
in '--dual_index' mode (see here: https://github.com/FelixKrueger/Umi-Grinder). UmiBam recognises
the UMIs within this pattern: R1:(ATCTAGTT):R2:(CAATTTTG): as (UMI R1) and (UMI R2).
--polyA This is a new, still experimental, trimming mode to identify and remove poly-A
tails from sequences.
When --polyA is selected, Trim Galore attempts to identify from the first supplied sample whether
sequences contain more often a stretch of either 'AAAAAAAAAA' or 'TTTTTTTTTT'. This determines if
Read 1 of a paired-end end file, or single-end files, are trimmed for PolyA or PolyT. In case of
paired-end sequencing, Read2 is trimmed for the complementary base from the start of the reads.
The auto-detection uses a default of A{20} for Read1 (3'-end trimming) and T{150} for Read2
(5'-end trimming). These values may be changed manually using the options -a and -a2.
In addition to trimming the sequences, white spaces are replaced with _ and it records in the read ID
how many bases were trimmed so it can later be used to identify PolyA trimmed sequences. This is
currently done by writing tags to both the start ("32:A:") and end ("_PolyA:32") of the reads in
the following example:
@READ-ID:1:1102:22039:36996 1:N:0:CCTAATCC
GCCTAAGGAAACAAGTACACTCCACACATGCATAAAGGAAATCAAATGTTATTTTTAAGAAAATGGAAAATAAAAACTTTATAAACACCAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
@32:A:READ-ID:1:1102:22039:36996_1:N:0:CCTAATCC_PolyA:32
GCCTAAGGAAACAAGTACACTCCACACATGCATAAAGGAAATCAAATGTTATTTTTAAGAAAATGGAAAATAAAAACTTTATAAACACC
PLEASE NOTE: The poly-A trimming mode expects that sequences were both adapter and quality trimmed
before looking for Poly-A tails, and it is the user's responsibility to carry out an initial round
of trimming. The following sequence:
1) trim_galore file.fastq.gz
2) trim_galore --polyA file_trimmed.fq.gz 3) zcat file_trimmed_trimmed.fq.gz | grep -A 3 PolyA |
grep -v ^-- > PolyA_trimmed.fastq
Will 1) trim qualities and Illumina adapter contamination, 2) find and remove PolyA contamination.
Finally, if desired, 3) will specifically find PolyA trimmed sequences to a specific FastQ file of
your choice.
--implicon This is a special mode of operation for paired-end data, such as required for the
IMPLICON method, where a UMI sequence
is getting transferred from the start of Read 2 to the readID of both reads. Following this, Trim
Galore will exit.
In it's current implementation, the UMI carrying reads come in the following format:
Read 1 5' FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF 3'
Read 2 3' UUUUUUUUFFFFFFFFFFFFFFFFFFFFFFFFFFFF 5'
Where UUUUUUUU is a random 8-mer unique molecular identifier (UMI) and FFFFFFF... is the actual fragment
to be
sequenced. The UMI of Read 2 (R2) is written into the read ID of both reads and removed from the
actual sequence. Here is an example:
R1: @HWI-D00436:407:CCAETANXX:1:1101:4105:1905 1:N:0: CGATGTTT
ATCTAGTTCAGTACGGTGTTTTCGAATTAGAAAAATATGTATAGAGGAAATAGATATAAAGGCGTATTCGTTATTG
R2: @HWI-D00436:407:CCAETANXX:1:1101:4105:1905 3:N:0: CGATGTTT
CAATTTTGCAGTACAAAAATAATACCTCCTCTATTTATCCAAAATCACAAAAAACCACCCACTTAACTTTCCCTAA
After --implicon trimming:
R1: @HWI-D00436:407:CCAETANXX:1:1101:4105:1905 1:N:0: CGATGTTT:CAATTTTG
ATCTAGTTCAGTACGGTGTTTTCGAATTAGAAAAATATGTATAGAGGAAATAGATATAAAGGCGTATTCGTTATTG
R2: @HWI-D00436:407:CCAETANXX:1:1101:4105:1905 3:N:0: CGATGTTT:CAATTTTG
CAGTACAAAAATAATACCTCCTCTATTTATCCAAAATCACAAAAAACCACCCACTTAACTTTCCCTAA
RRBS-specific options (MspI digested material):
--rrbs Specifies that the input file was an MspI digested RRBS sample (recognition
site: CCGG). Single-end or Read 1 sequences (paired-end) which were adapter-trimmed
will have a further 2 bp removed from their 3' end. Sequences which were merely trimmed because of
poor quality will not be shortened further. Read 2 of paired-end libraries will in addition have
the first 2 bp removed from the 5' end (by setting '--clip_r2 2'). This is to avoid using
artificial methylation calls from the filled-in cytosine positions close to the 3' MspI site in
sequenced fragments. This option is not recommended for users of the NuGEN ovation RRBS System
1-16 kit (see below).
--non_directional Selecting this option for non-directional RRBS libraries will screen
quality-trimmed sequences for 'CAA' or 'CGA' at the start of the read
and, if found, removes the first two basepairs. Like with the option '--rrbs' this avoids using
cytosine positions that were filled-in during the end-repair step. '--non_directional' requires
'--rrbs' to be specified as well. Note that this option does not set '--clip_r2 2' in paired-end
mode.
--keep Keep the quality trimmed intermediate file. Default: off, which means
the temporary file is being deleted after adapter trimming. Only has
an effect for RRBS samples since other FastQ files are not trimmed for poor qualities separately.
Note for RRBS using the NuGEN Ovation RRBS System 1-16 kit:
Owing to the fact that the NuGEN Ovation kit attaches a varying number of nucleotides (0-3) after each
MspI site Trim Galore should be run WITHOUT the option --rrbs. This trimming is accomplished in a
subsequent diversity trimming step afterwards (see their manual).
Note for RRBS using MseI:
If your DNA material was digested with MseI (recognition motif: TTAA) instead of MspI it is NOT necessary
to specify --rrbs or --non_directional since virtually all reads should start with the sequence 'TAA',
and this holds true for both directional and non-directional libraries. As the end-repair of 'TAA'
restricted sites does not involve any cytosines it does not need to be treated especially. Instead,
simply run Trim Galore! in the standard (i.e. non-RRBS) mode.
Paired-end specific options:
--paired This option performs length trimming of quality/adapter/RRBS trimmed reads for
paired-end files. To pass the validation test, both sequences of a sequence pair
are required to have a certain minimum length which is governed by the option --length (see
above). If only one read passes this length threshold the other read can be rescued (see option
--retain_unpaired). Using this option lets you discard too short read pairs without disturbing the
sequence-by-sequence order of FastQ files which is required by many aligners.
Trim Galore! expects paired-end files to be supplied in a pairwise fashion, e.g.
file1_1.fq file1_2.fq SRR2_1.fq.gz SRR2_2.fq.gz ... .
-t/--trim1 Trims 1 bp off every read from its 3' end. This may be needed for FastQ files
that
are to be aligned as paired-end data with Bowtie. This is because Bowtie (1) regards
alignments like this:
R1 --------------------------->
or this: -----------------------> R1
R2 <---------------------------
<----------------- R2
as invalid (whenever a start/end coordinate is contained within the other read).
NOTE: If you are planning to use Bowtie2, BWA etc. you don't need to specify this option.
--retain_unpaired If only one of the two paired-end reads became too short, the longer
read will be written to either '.unpaired_1.fq' or '.unpaired_2.fq'
output files. The length cutoff for unpaired single-end reads is governed by the parameters
-r1/--length_1 and -r2/--length_2. Default: OFF.
-r1/--length_1 <INT> Unpaired single-end read length cutoff needed for read 1 to be written to
'.unpaired_1.fq' output file. These reads may be mapped in single-end mode.
Default: 35 bp.
-r2/--length_2 <INT> Unpaired single-end read length cutoff needed for read 2 to be written to
'.unpaired_2.fq' output file. These reads may be mapped in single-end mode.
Default: 35 bp.
Last modified on 07 October 2020.
AUTHOR
This manpage was written by Nilesh Patra for the Debian distribution and
can be used for any other usage of the program.
trim_galore 0.6.7 July 2021 TRIM_GALORE(1)