Inputs

  1. Overview
  2. Input Options
    1. --input
      1. Example samplesheet
      2. Samplesheet columns
    2. --max_reads
    3. --max_depth
  3. Database Options
    1. --db
    2. --push
  4. Asset Options
    1. --gambit_gdb
    2. --gambit_gs
    3. --microreact_template
  5. Clustering Options
    1. --clust_dist
    2. --clust_min_hash_freq
    3. --clust_min_hash_frac
    4. --clust_ignore_qc
    5. --clust_overwrite
    6. --clust_plot
    7. This can be helpful for interpreting cluster relationships. May take a significant amount of time when there are many samples!
  6. Reference Selection Options
    1. --ref_min_contig_len
    2. --ref_contig_penalty
    3. --ref_ksize
    4. --ref_scaled
  7. Variant Calling Options
    1. --min_genome_fraction
    2. --min_core_fraction
    3. --mask_recomb
    4. --keep_bam
  8. Phylogenetic Analysis Options
    1. --min_tree
    2. --strong_link_threshold
    3. --inter_link_threshold
    4. --partition_distance

Overview

Pipeline parameters can be adjusted using the following methods:

  1. At the command line using --{parameter_name} (e.g., --input)
  2. In the nextflow.config file
  3. In a JSON file via the -params-file parameter

It is also possible to pass arguments directly to a pipeline process using the ext.args variable in conf/modules.config (see example below):

    withName: 'IVAR_CONSENSUS' {
        ext.args            = "-n 'N' -k"
        ext.when            = {  }
        publishDir = [
            [
                path: { "${params.outdir}/${meta.id}/assembly/" },
                pattern: "none",
                mode: 'copy'
            ],
            [
                path: { "${params.outdir}/${meta.id}/qc" },
                pattern: "*.csv",
                mode: 'copy'
            ]
        ]
    }

Input Options

--input

Path to the samplesheet.

Example samplesheet

samplesheet.csv:

sample,fastq_1,fastq_2
sample01,sample01_R1_001.fastq.gz,sample01_R2_001.fastq.gz
sample02,sample02_R1_001.fastq.gz,sample02_R2_001.fastq.gz

Samplesheet columns

  • Required columns: sample, and fastq_1 + fastq_2 or sra
  • All file paths in the samplesheet must be absolute.
Column Name Description
sample Sample name
fastq_1 Absolute path to the forward (R1) Illumina read file (.fq or .fastq). Must be supplied with fastq_2. Cannot be supplied with sra column.
fastq_2 Absolute path to the reverse (R2) Illumina read file (.fq or .fastq). Must be supplied with fastq_1. Cannot be supplied with sra column.
assembly Absolute path to an existing assembly file (.fasta or .fa). If provided, assembly will be skipped for this sample.
taxon Taxonomic name of the sample (e.g., Staphylococcus aureus). If provided, taxonomic classification will be skipped for this sample.
sra SRA accession number (e.g., SRR12345678). Cannot be supplied with fastq_1 or fastq_2 columns.
genbank GenBank accession number of a reference genome to use for this sample. Overrides automatic reference selection.
cluster Pre-assigned cluster ID for this sample. If provided, cluster assignment will be skipped for this sample.

--max_reads

The maximum number of reads to include in the analysis.

  • Options: 0...Inf
  • Default: 2_000_000

Samples with more than this number of reads will be randomly down-sampled using seqtk sample. Read counts are based on the sum of the forward and reverse reads.

--max_depth

The maximum sequencing depth per sample.

  • Options: 0...Inf
  • Default: 100

Impacts de novo assembly and variant calling. Samples exceeding this depth will be down-sampled prior to these steps.

Database Options

--db

Path to the BigBacter surveillance database.

  • Default: bigbacter_db

This database stores signatures, cluster assignments, and other persistent outputs across runs.

--push

Whether to push results to the BigBacter database after the run.

  • Options: true, false
  • Default: false

When enabled, results are written to --db so they are included in future runs. Commonly used with --resume to push results from a previous run without recomputing them.

Asset Options

--gambit_gdb

Path to the GAMBIT database file used for taxonomic classification.

  • Default: https://storage.googleapis.com/jlumpe-gambit/public/databases/refseq-curated/1.0/gambit-refseq-curated-1.0.gdb

Used to classify samples when no taxon is provided in the samplesheet.

--gambit_gs

Path to the GAMBIT database file used for taxonomic classification.

  • Default: https://storage.googleapis.com/jlumpe-gambit/public/databases/refseq-curated/1.0/gambit-refseq-curated-1.0.gs

Used to classify samples when no taxon is provided in the samplesheet.

--microreact_template

Path to the Microreact template JSON file used for visualization.

  • Default: ${projectDir}/assets/template.microreact

Clustering Options

--clust_dist

Distance threshold used to define clusters.

  • Options: 0...1
  • Default: 0.03

Samples with a pairwise distance below this threshold will be assigned to the same cluster.

--clust_min_hash_freq

Minimum frequency for a hash to be included in the global hash set.

  • Options: 0...1
  • Default: 0.05

Hashes occurring below this frequency across all samples are excluded from the global reference set.

--clust_min_hash_frac

Minimum fraction of sample hashes that must overlap with the global hash set after filtering.

  • Options: 0...1
  • Default: 0.5

Samples falling below this threshold may indicate low-quality or divergent sequences.

--clust_ignore_qc

Whether to ignore clustering QC results and include all samples regardless of QC status.

  • Options: true, false
  • Default: false

When enabled, samples that would otherwise fail clustering QC are still included in the analysis.

--clust_overwrite

Whether to overwrite existing signature files for a sample.

  • Options: true, false
  • Default: false

By default, signature files are reused if they already exist in --db. Enable this to force regeneration.

--clust_plot

Whether to create PCoA and Neighbor-joining plots when running floc.

  • Options: true, false
  • Default: false

This can be helpful for interpreting cluster relationships. May take a significant amount of time when there are many samples!

Reference Selection Options

--ref_min_contig_len

Minimum contig length (bp) allowed in a reference genome.

  • Options: 0...Inf
  • Default: 300

Contigs shorter than this value are excluded from the reference prior to analysis.

--ref_contig_penalty

Penalty applied to references with more contigs during reference selection scoring.

  • Options: 0...1
  • Default: 0.2

Higher values more strongly penalize fragmented references. A score of 0 applies no penalty.

--ref_ksize

K-mer size used when comparing references.

  • Options: 0...Inf
  • Default: 31

--ref_scaled

K-mer scaling factor used when comparing references.

  • Options: 0...Inf
  • Default: 100

Higher values reduce memory usage at the cost of resolution. Used by the sourmash sketching step.

Variant Calling Options

--min_genome_fraction

Minimum fraction of the reference genome that must be covered for a sample to be included in core genome analysis.

  • Options: 0...1
  • Default: 0.8

Samples falling below this threshold are excluded from variant calling and downstream phylogenetic analysis.

--min_core_fraction

Minimum fraction of samples that must have coverage at a reference site for it to be included in the core genome.

  • Options: 0...1
  • Default: 0.9

Sites with coverage in fewer samples than this threshold are excluded from the core genome alignment.

--mask_recomb

Whether to perform recombination masking in addition to standard variant detection.

  • Options: true, false
  • Default: true

When enabled, recombinant regions identified by Gubbins are masked prior to phylogenetic analysis.

--keep_bam

Keep the bam file created during variant calling.

  • Options: true, false
  • Default: false

Enabling will dramatically increase database size.

Phylogenetic Analysis Options

--min_tree

Minimum number of samples required in a core genome analysis to produce a phylogenetic tree.

  • Options: 2...Inf
  • Default: 2

Must be greater than 1. Clusters with fewer samples than this value will not have a tree generated.

--strong_link_threshold

Upper nucleotide distance threshold for defining a strong linkage between two samples.

  • Options: 0...Inf
  • Default: 10

Sample pairs with SNP distances from 0 to this value are classified as strongly linked.

--inter_link_threshold

Upper nucleotide distance threshold for defining an intermediate linkage between two samples.

  • Options: 0...Inf
  • Default: 50

Sample pairs with SNP distances from --strong_link_threshold + 1 to this value are classified as intermediately linked.

--partition_distance

Nucleotide distance threshold for grouping samples into tree partitions.

  • Options: 0...Inf
  • Default: 100

Samples within this SNP distance of one another are grouped into the same partition for visualization.

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