fgbio

Tools for working with genomic and high throughput sequencing data.

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DemuxFastqs

Overview

Group: FASTQ

Performs sample demultiplexing on FASTQs.

The sample barcode for each sample in the sample sheet will be compared against the sample barcode bases extracted from the FASTQs, to assign each read to a sample. Reads that do not match any sample within the given error tolerance will be placed in the ‘unmatched’ file.

The type of output is specified with the --output-type option, and can be BAM (--output-type BamOnly), gzipped FASTQ (--output-type FastqOnly), or both (--output-type Both).

For BAM output, the output directory will contain one BAM file per sample in the sample sheet or metadata CSV file, plus a BAM for reads that could not be assigned to a sample given the criteria. The output file names will be the concatenation of sample id, sample name, and sample barcode bases (expected not observed), delimited by -. A metrics file will also be output providing analogous information to the metric described SampleBarcodeMetric.

For gzipped FASTQ output, one or more gzipped FASTQs per sample in the sample sheet or metadata CSV file will be written to the output directory. For paired end data, the output will have the suffix _R1.fastq.gz and _R2.fastq.gz for read one and read two respectively. The sample barcode and molecular barcodes (concatenated) will be appended to the read name and delimited by a colon. If the --illumina-standards option is given, then the output read names and file names will follow the Illumina standards described here.

The output base qualities will be standardized to Sanger/SAM format.

FASTQs and associated read structures for each sub-read should be given:

If multiple FASTQs are present for each sub-read, then the FASTQs for each sub-read should be concatenated together prior to running this tool (ex. cat s_R1_L001.fq.gz s_R1_L002.fq.gz > s_R1.fq.gz).

(Read structures)[https://github.com/fulcrumgenomics/fgbio/wiki/Read-Structures] are made up of <number><operator> pairs much like the CIGAR string in BAM files. Four kinds of operators are recognized:

  1. T identifies a template read
  2. B identifies a sample barcode read
  3. M identifies a unique molecular index read
  4. S identifies a set of bases that should be skipped or ignored

The last <number><operator> pair may be specified using a + sign instead of number to denote “all remaining bases”. This is useful if, e.g., fastqs have been trimmed and contain reads of varying length. Both reads must have template bases. Any molecular identifiers will be concatenated using the - delimiter and placed in the given SAM record tag (RX by default). Similarly, the sample barcode bases from the given read will be placed in the BC tag.

Metadata about the samples should be given in either an Illumina Experiment Manager sample sheet or a metadata CSV file. Formats are described in detail below.

The read structures will be used to extract the observed sample barcode, template bases, and molecular identifiers from each read. The observed sample barcode will be matched to the sample barcodes extracted from the bases in the sample metadata and associated read structures.

Sample Sheet

The read group’s sample id, sample name, and library id all correspond to the similarly named values in the sample sheet. Library id will be the sample id if not found, and the platform unit will be the sample name concatenated with the sample barcode bases delimited by a ..

The sample section of the sample sheet should contain information related to each sample with the following columns:

Metadata CSV

In lieu of a sample sheet, a simple CSV file may be provided with the necessary metadata. This file should contain the same columns as described above for the sample sheet (Sample_ID, Sample_Name, Library_ID, and Description).

Example Command Line

As an example, if the sequencing run was 2x100bp (paired end) with two 8bp index reads both reading a sample barcode, as well as an in-line 8bp sample barcode in read one, the command line would be

--inputs r1.fq i1.fq i2.fq r2.fq --read-structures 8B92T 8B 8B 100T \
    --metadata SampleSheet.csv --metrics metrics.txt --output output_folder

Output Standards

The following options affect the output format:

  1. If --omit-fastq-read-numbers is specified, then trailing /1 and /2 for R1 and R2 respectively, will not be appended to e FASTQ read name. By default they will be appended.
  2. If --include-sample-barcodes-in-fastq is specified, then sample barcode will replace the last field in the first comment in the FASTQ header, e.g. replace ‘NNNNNN’ in the header @Instrument:RunID:FlowCellID:Lane:Tile:X:Y 1:N:0:NNNNNN
  3. If --illumina-file-names is specified, the output files will be named according to the Illumina FASTQ file naming conventions:

a. The file extension will be _R1_001.fastq.gz for read one, and _R2_001.fastq.gz for read two (if paired end). b. The per-sample output prefix will be <SampleName>_S<SampleOrdinal>_L<LaneNumber> (without angle brackets).

Options (1) and (2) require the input FASTQ read names to contain the following elements:

@<instrument>:<run number>:<flowcell ID>:<lane>:<tile>:<x-pos>:<y-pos> <read>:<is filtered>:<control number>:<index>

See the Illumina FASTQ conventions for more details.

The --illumina-standards option may not be specified with the three options above. Use this option if you intend to upload to Illumina BaseSpace. This option implies:

--omit-fastq-read-numbers=true --include-sample-barcodes-in-fastq=false --illumina-file-names=true

See the Illumina Basespace standards described here.

To output with recent Illumina conventions (circa 2021) that match bcl2fastq and BCLconvert, use:

--omit-fastq-read-numbers=true --include-sample-barcodes-in-fastq=true --illumina-file-names=true

By default all input reads are output. If your input FASTQs contain reads that do not pass filter (as defined by the Y/N filter flag in the FASTQ comment) these can be filtered out during demultiplexing using the --omit-failing-reads option.

To output only reads that are not control reads, as encoded in the <control number> field in the header comment, use the --omit-control-reads flag

Arguments

Name Flag Type Description Required? Max Values Default Value(s)
inputs i PathToFastq One or more input fastq files each corresponding to a sub-read (ex. index-read, read-one, read-two, fragment). Required Unlimited  
output o DirPath The output directory in which to place sample BAMs. Required 1  
metadata x FilePath A file containing the metadata about the samples. Required 1  
read-structures r ReadStructure The read structure for each of the FASTQs. Required Unlimited  
metrics m FilePath The file to which per-barcode metrics are written. If none given, a file named demux_barcode_metrics.txt will be written to the output directory. Optional 1  
column-for-sample-barcode c String The column name in the sample sheet or metadata CSV for the sample barcode. Optional 1 Sample_Barcode
unmatched u String Output BAM file name for the unmatched records. Optional 1 unmatched.bam
quality-format q QualityEncoding A value describing how the quality values are encoded in the FASTQ. Either Solexa for pre-pipeline 1.3 style scores (solexa scaling + 66), Illumina for pipeline 1.3 and above (phred scaling + 64) or Standard for phred scaled scores with a character shift of 33. If this value is not specified, the quality format will be detected automatically. Optional 1  
threads t Int The number of threads to use while de-multiplexing. The performance does not increase linearly with the # of threads and seems not to improve beyond 2-4 threads. Optional 1 1
max-mismatches   Int Maximum mismatches for a barcode to be considered a match. Optional 1 1
min-mismatch-delta   Int Minimum difference between number of mismatches in the best and second best barcodes for a barcode to be considered a match. Optional 1 2
max-no-calls   Int Maximum allowable number of no-calls in a barcode read before it is considered unmatchable. Optional 1 2
sort-order   SortOrder The sort order for the output sam/bam file (typically unsorted or queryname). Optional 1 queryname
umi-tag   String The SAM tag for any molecular barcode. If multiple molecular barcodes are specified, they will be concatenated and stored here. Optional 1 RX
platform-unit   String The platform unit (typically <flowcell-barcode>-<sample-barcode>.<lane>) Optional 1  
sequencing-center   String The sequencing center from which the data originated Optional 1  
predicted-insert-size   Integer Predicted median insert size, to insert into the read group header Optional 1  
platform-model   String Platform model to insert into the group header (ex. miseq, hiseq2500, hiseqX) Optional 1  
platform   String Platform to insert into the read group header of BAMs (e.g Illumina) Optional 1 Illumina
comments   String Comment(s) to include in the merged output file’s header. Optional Unlimited  
run-date   Iso8601Date Date the run was produced, to insert into the read group header Optional 1  
output-type   OutputType The type of outputs to produce. Optional 1  
include-all-bases-in-fastqs   Boolean Output all bases (i.e. all sample barcode, molecular barcode, skipped, and template bases) for every read with template bases (ex. read one and read two) as defined by the corresponding read structure(s). Optional 1 false
illumina-standards   Boolean Output FASTQs according to Illumina BaseSpace Sequence Hub naming standards. This is differfent than Illumina naming standards. Optional 1 false
omit-fastq-read-numbers   Boolean Do not include trailing /1 or /2 for R1 and R2 in the FASTQ read name. Optional 1 false
include-sample-barcodes-in-fastq   Boolean Insert the sample barcode into the FASTQ header. Optional 1 false
illumina-file-names   Boolean Name the output files according to the Illumina file name standards. Optional 1 false
omit-failing-reads   Boolean Keep only passing filter reads if true, otherwise keep all reads. Passing filter reads are determined from the comment in the FASTQ header. Optional 1 false
omit-control-reads   Boolean Do not keep reads identified as control if true, otherwise keep all reads. Control reads are determined from the comment in the FASTQ header. Optional 1 false
mask-bases-below-quality   Int Mask bases with a quality score below the specified threshold as Ns Optional 1 0