BamToFastq Nextflow Workflow

Convert BAM files back to FASTQ.

Quickstart with Conda

We do not recommend Conda for running the workflow. It may happen that packages are not available in any channels anymore and that the environment is broken. For reproducible research, please use containers.

Provided you have a working Conda installation, you can run the workflow with

mkdir test_out/
nextflow run main.nf \
    -profile local,conda \
    -ansi-log \
    --input=/path/to/your.bam \
    --outputDir=test_out \
    --sortFastqs=false

For each BAM file in the comma-separated --input parameter, one directory with FASTQs is created in the outputDir. With the local profile the processing jobs will be executed locally. The conda profile will let Nextflow create a Conda environment from the task-environment.yml file. By default, the conda environment will be created in the source directory of the workflow (see nextflow.config).

Quickstart with Docker

Dependent on the version of the workflow that you want to run it might not be possible to re-build the Conda environment. Therefore, to guarantee reproducibility we create container images of the task environment.

For instance, if you want to run the workflow locally with Docker you can do e.g.

nextflow run main.nf \
    -profile local,docker \
    -ansi-log \
    --input=test/test1_paired.bam,test/test1_unpaired.bam \
    --outputDir=test_out \
    --sortFastqs=true

Quickstart with Singularity

In your cluster, you may not have access to Docker. In this situation you can use Singularity, if it is installed in your cluster. Note that unfortunately, Nextflow will fail to convert the Docker image into a Singularity image, unless Docker is available. But you can get the Singularity image yourself:

1. Create a Singularity image from the public Docker container

   version=1.0.0
   repoDir=/path/to/nf-bam2fastq
   singularity build \
     "$repoDir/cache/singularity/nf-bam2fastq_$version.sif" \
     "docker://ghcr.io/dkfz-odcf/nf-bam2fastq:$version"

   Note that the location and name of the Singularity image is configured in the nextflow.config.

2. Now, you can run the workflow with the “singularity” profile, e.g. on an LSF cluster:

   nextflow run /path/to/nf-bam2fastq/main.nf \
     -profile lsf,singularity \
     -ansi-log \
     --input=test/test1_paired.bam,test/test1_unpaired.bam \
     --outputDir=test_out \
     --sortFastqs=true

Remarks

• By default, the workflow sorts FASTQ files by their IDs to avoid e.g. that reads extracted from position-sorted BAMs are fed into the next processing step (possibly re-alignment) in a sorting order that may affect the processing. For instance, keeping position-based sorting order may result in systematic fluctuations of the average insert-size distributions in the FASTQ stream. Note, however, that most jobs of the workflow are actually sorting-jobs — so you can save a lot of computation time, if the input order during alignment does not matter for you. And if you don’t worry about such problems during alignment, you may save a lot of additional time during sorting of the already almost-sorted alignment output.
• Obviously, you can only reconstitute complete original FASTQs (except for order), if the BAM was not filtered in any way, e.g. by removing duplicated reads, read trimming, of if the input file is truncated.
• Paired-end FASTQs are generated with biobambam2‘s bamtofastq.
• Sorting is done with the UNIX coreutils tool “sort” in an efficient way (e.g. sorting per read-group; co-sorting of order-matched mate FASTQs).

Status

Please have a look at the project board for further information.

Parameters

Required parameters

• input: Comma-separated list of input BAM-file paths.
• outputDir: Output directory

Optional parameters

• sortFastqs: Whether to produce FASTQs in a similar order as in the input BAM (false) or sort by name (true). Default: true. Turning sorting on produces multiple sort-jobs.
• excludedFlags: Comma-separated list of flags to bamtofastq‘s exclude parameter. Default: “secondary,supplementary”. If you have complete, BWA-aligned BAM files then exactly the reads of the input FASTQ are reproduced. For other aligners you need to check yourself, what are the optimal parameters.
• publishMode: Nextflow’s publish mode. Allowed values are symlink , rellink, link, copy, copyNoFollow, move. Default is rellink, which produces relative links from the publish dir (in the outputDir) to the directories in the work/ directory. This is to support an invocation of Nextflow in a “run” directory in which all files (symlinked input data, output data, logs) are stored together (e.g. with nextflow run --outputDir ./).
• Trading memory vs. I/O
  • sortMemory: Memory used for sorting. Too large values are useless, unless you have enough memory to sort completely in-memory. Default: “100 MB”.
  • sortThreads: Number of threads used for sorting. Default: 4.
  • compressIntermediateFastqs: Whether to compress FASTQs produced by bamtofastq when doing subsequent sorting. Default: true. This is only relevant if sortFastq=true.
  • compressorThreads: The compressor (pigz) can use multiple threads. Default: 4. If you set this value to zero, then no additional CPUs are required by Nextflow to be present. However, a single thread still will be used by pigz.

Output

In the outputDir the workflow creates a sub-directory for each input BAM file. These are named like the BAM with one of the suffixes _fastqs or _sorted_fastqs added, dependent on the value for sortFastqs you selected. Each of these directories contains a set of FASTQ files, whose names follow the pattern

${readGroupName}_${readType}.fastq.gz

The read-group name is the name of the “@RG” attribute the reads in the file were found to be connected to. For reads in your BAM that don’t have a read-group assigned the “default” read-group is used. Consequently, your BAMs should not contain a read-group “default”! The read-type is one of the following:

• R1, R2: paired-reads 1 or 2
• U1, U2: orphaned reads, i.e. first or second reads marked as paired but with a missing mate.
• S: single-end reads

These files are all always produced, independent of whether your data is actually single-end or paired-end. If no reads of any of these groups are present in the input BAM file, empty compressed files are produced. Note further that these files are produced for each read-group in your input BAM, plus the “default” read-group. If you have a BAM in which none of the reads are assigned to a read-group, then all reads can be found in the “default” read-group.

Note that Nextflow creates the work/ directory, the .nextflow/ directory, and the .nextflow.log* files in the directory in which it is executed.

Environment and Execution

Nextflow‘s -profile parameter allows setting technical options for executing the workflow. You have already seen some of the profiles and that these can be combined. We conceptually separated the predefined profiles into two types — those concerning the “environment” and those for selecting the “executor”.

The following “environment” profiles that define which environment will be used for executing the jobs are predefined in the nextflow.config:

• conda
• mamba
• docker
• singularity

Currently, there are only two “executor” profiles that define the job execution method. These are

• local: Just execute the jobs locally on the system that executes Nextflow.
• lsf: Submit the jobs to an LSF cluster. Nextflow must be running on a cluster node on which bsub is available.

Please refer to the Nextflow documentation for defining other executors. Note that environments and executors cannot arbitrarily be combined. For instance, your LSF administrators may not allow Docker to be executed by normal users.

Location of Environments

By default, the Conda environments of the jobs as well as the Singularity containers are stored in subdirectories of the cache/ subdirectory of the workflows installation directory (a.k.a projectDir by Nextflow). E.g. to use the Singularity container you can install the container as follows

cd $workflowRepoDir
# Refer to the nextflow.config for the name of the Singularity image.
singularity build \
  cache/singularity/nf-bam2fastq_1.0.0.sif \
  docker://ghcr.io/dkfz-odcf/nf-bam2fastq:1.0.0
# Test your container
test/test1.sh test-results/ singularity nextflowEnv/

This is suited for either a user-specific installation or for a centralized installation for which the environments should be shared for all users. Please refer to the nextflow.config or the NXF_*_CACHEDIR environment variables to change this default (see here.

Make sure your users have read and execute permissions on the directories and read permissions on the files in the shared environment directories. Set NXF_CONDA_CACHEDIR to an absolute path to avoid “Not a conda environment: path/to/env/nf-bam2fastq-3e98300235b5aed9f3835e00669fb59f” errors.

Development

The integration tests can be run with

test/test1.sh test-results/ $profile

This will create a test Conda environment in test-results/nextflowEnv and then run the tests. For the tests themselves you can use a local Conda environment or a Docker container, dependent on whether you set $profile to “conda” or “docker”, respectively. These integration tests are also run in Travis CI.

Continuous Delivery

For all commits with a tag that follows the pattern \d+\.\d+\.\d+ the job containers are automatically pushed to Github Container Registry of the “ODCF” organization. Version tags should only be added to commits on the master branch, although currently no automatic rule enforces this.

Manual container release

The container includes a Conda installation and is pretty big. It should only be released if its content is actually changed. For instance, it would be perfectly fine to have a workflow version 1.6.5 but still refer to an old container for 1.2.7.

This is an outline of the procedure to release the container to Github Container Registry:

1. Set the version that you want to release as variable. For the later commands you can set the Bash variable

   versionTag=1.2.0

2. Build the container.

   docker \
      build \
      -t ghcr.io/dkfz-odcf/nf-bam2fastq:$versionTag \
      --build-arg HTTP_PROXY=$HTTP_PROXY \
      --build-arg HTTPS_PROXY=$HTTPS_PROXY \
      ./

3. Edit the version-tag for the docker container in the “docker”-profile in the nextflow.config to match $versionTag.
4. Run the integration test with the new container

   test/test1.sh docker-test docker

5. If the test succeeds, push the container to Github container registry. Set the CR_PAT variable to your personal access token (PAT):

   echo $CR_PAT | docker login ghcr.io -u vinjana --password-stdin
   docker image push ghcr.io/dkfz-odcf/nf-bam2fastq:$versionTag

Release Notes

• 1.2.0

  • Minor: Updated to miniconda3:4.10.3 base container, because the previous version (4.9.2) didn’t build anymore.
  • Minor: Use -env none for “lsf” cluster profile. Local environment should not be copied. This probably caused problems with the old “dkfzModules” environment profile.
  • Patch: Require Nextflow >= 22.07.1, which fixes an LSF memory request bug. Added options for per-job memory requests to “lsf” profile in nextflow.config.
  • Patch: Remove unnecessary *_BINARY variables in scripts. Binaries are fixed by Conda/containers.
  • Patch: Needed to explicitly set conda.enabled = True with newer Nextflow

• 1.1.0 (February, 2022)

  • Minor: Added --publishMode option to allow user to select the Nextflow publish mode. Default: rellink. Note that the former default was symlink, but as this change is considered negligible we classified the change as “minor”.
  • Minor: Removed dkfzModules profile. Didn’t work well and was originally only for development. Please use ‘conda’, ‘singularity’ or ‘docker’. The container-based environments provide the best reproducibility.
  • Patch: Switched from Travis to CircleCI for continuous integration.

• 1.0.1 (October 14., 2021)

  • Patch: Fix memory calculation as exponential backoff
  • Patch: Job names now contain workflow name and job/task hash. Run name seems currently not possible to include there (due to a possible bug in Nextflow).
  • Patch: The end message when the workflow runs now reports whether the workflow execution failed (instead of always “success”).

• 1.0.0 (June 15., 2021)

  • Adapted resource expressions to conservative values.
  • Reduced resources for integration tests (threads and memory).
  • Bugfix: Set sorting memory.
  • Update to biobambam 2.0.179 to fix its orphaned second-reads bug
  • Changes to make workflow more nf-core conformant
    • Rename bam2fastq.nf to main.nf (similar to nf-core projects)
    • Rename --bamFiles to --input parameter

• 0.2.0 (November 17., 2020)

  • Added integration tests
  • CI via travis-ci
  • NOTE: Due to a bug in the used biobambam version 2.0.87 the orphaned second-read file is not written. See here. An update to 2.0.177+ is necessary.

• 0.1.0 (August 26., 2020)

  • Working but not deeply tested base version

Origins

The workflow is a port of the Roddy-based BamToFastqPlugin. Compared to the Roddy-workflow, some problems with the execution of parallel processing, resulting in potential errors, have been fixed.

License & Contributors

See LICENSE.txt and CONTRIBUTORS.