trimmomatic

The current trimming steps are:

ILLUMINACLIP: Cut adapter and other illumina-specific sequences from the read. SLIDINGWINDOW: Perform a sliding window trimming, cutting once the average quality within the window falls below a threshold.

LEADING: Cut bases off the start of a read, if below a threshold quality

TRAILING: Cut bases off the end of a read, if below a threshold quality

CROP: Cut the read to a specified length

HEADCROP: Cut the specified number of bases from the start of the read

MINLEN: Drop the read if it is below a specified length

TOPHRED33: Convert quality scores to Phred-33

TOPHRED64: Convert quality scores to Phred-64

It works with FASTQ (using phred + 33 or phred + 64 quality scores, depending on the Illumina pipeline used), either uncompressed or gzipp'ed FASTQ. Use of gzip format is determined based on the .gz extension.

For single-ended data, one input and one output file are specified, plus the processing steps. For paired-end data, two input files are specified, and 4 output files, 2 for the 'paired' output where both reads survived the processing, and 2 for corresponding 'unpaired' output where a read survived, but the partner read did not.

Trimmomatic is a java program accessed via a modules library on the lab cluster.

module load trimmomatic

This loads the default version of Trimmomatic and sets the environment variable TRIMMOMATIC.

Then invoke the program:

java -jar $TRIMMOMATIC/trimmomatic.jar

java -Xmx2000M -jar $TRIMMOMATIC/trimmomatic.jar PE R1.fastq R2.fastq R1.PE.fastq R1.SE.fastq R2.PE.fastq R2.SE.fastq ILLUMINACLIP:$TRIMMOMATIC/adapters/NexteraPE-PE.fa:2:30:10:2:true LEADING:3 TRAILING:3 SLIDINGWINDOW:4:15 MINLEN:30 

The user manual is available at http://www.usadellab.org/cms/uploads/supplementary/Trimmomatic/TrimmomaticManual_V0.32.pdf

Consider using the risstrim.pl script in the riss_util module, which provides a simplified interface for running Trimmomatic.

module load riss_util
risstrim.pl -h