StrainQuant

Introduction

StrainQuant is a Nextflow pipeline for performing strain-specific bacterial RNA-Seq analysis without a reference genome.

Pipeline summary

The pipeline requires the output from a pan-genome analysis with Panaroo and will perform the following steps:

1. Trim adaptors from reads (Trim Galore!)
2. Read QC (FastQC)
3. Subset to genes of interest (e.g. the core gene set; or by majority sequence type)
4. Pseudo-alignment to strain-specific gene sets (kallisto)
5. Merging and length-scaling of counts for orthologous genes
6. Size-factor scaling of merged counts (DESeq2 or edgeR)
7. Visualisation of gene expression across strains (UMAP)

Installation

You will need to install Nextflow (version 21.10.3+).

You can run the pipeline as follows:

nextflow run /path/to/StrainQuant \
    --meta_file /path/to/metadata.txt \
    --gpa_file /path/to/gene_presence_absence.csv \
    --perc 99 --norm_method DESeq --group majority_ST \
    -profile conda -resume

You can run with Docker or Singularity by specifying -profile docker or -profile singularity, respectively.

The -resume parameter will re-start the pipeline if it has been previously run.

Explanation of parameters:

• meta_file: metadata file (see below).
• gpa_file: gene presence/absence file from Panaroo (see below).
• perc: defines the minimum percent of strains containing a gene for inclusion in the analysis (for example, --perc 99 means that a gene must be present in 99% of strains for it to be included).
• strandedness: Strandedness of the reads. 0 = unstranded, 1 = forward-stranded, 2 = reverse-stranded. Default = 2.
• fragment_len: Estimated average fragment length for kallisto transcript quantification (only required for single-end reads). Default = 150.
• fragment_sd: Estimated standard deviation of fragment length for kallisto transcript quantification (only required for single-end reads). Default = 20.
• norm_method: how to perform size-factor scaling of counts (default method = DESeq2). Other options: TMM (edgeR).
• group: group for plots - must be one of the columns in metadata file.
• skip_trimming: do not trim adaptors from reads.
• outdir: the output directory where the results will be saved (Default: ./results).

Required input

• Metadata file: tab-delimited (TSV) file, which must contain at least the following named columns:

  • rna_sample_id: name of the RNA-Seq data file
  • dna_sample_id: gene sequence sample identifier (must match the column name in the Panaroo gene presence/absence file)
  • sample_name: unique identifier for the sample
  • fastq1: path to fastq file for RNA-Seq data
  • fastq2: (optional) path to 2nd fastq file for paired-end RNA-Seq data - leave blank for single-end data
  • fasta: path to fasta file containing gene sequences
  • Additional columns are optional

  Example:

  rna_sample_id	dna_sample_id	sample_name	majority_ST	level7000	acsA	aroE	guaA	mutL	nuoD	ppsA	trpE	patient	collection_date	cohort	infection_type	fastq1	fastq2	fasta
  SRX5123742	SRR8737281	ZG301975	313	2	47	8	7	6	8	11	40	ZG301975		hzi_amr		https://raw.githubusercontent.com/adamd3/StrainQuant/main/test_data/SRX5123742_T1_sub.fq.gz		https://raw.githubusercontent.com/adamd3/StrainQuant/main/test_data/SRR8737281.fna
  SRX5123741	SRR8737282	ZG205864	111	3	17	5	5	4	4	4	3	ZG205864		hzi_amr		https://raw.githubusercontent.com/adamd3/StrainQuant/main/test_data/SRX5123741_T1_sub.fq.gz		https://raw.githubusercontent.com/adamd3/StrainQuant/main/test_data/SRR8737282.fna
  SRX5123744	SRR8737283	ZG302367	274	4	23	5	11	7	1	12	7	ZG302367		hzi_amr	ear infection	https://raw.githubusercontent.com/adamd3/StrainQuant/main/test_data/SRX5123744_T1_sub.fq.gz		https://raw.githubusercontent.com/adamd3/StrainQuant/main/test_data/SRR8737283.fna

• Gene presence-absence file: CSV-format output produced by Panaroo. See below example (truncated):

  Gene,Non-unique Gene name,Annotation,Pseudomonas_aeruginosa_PAO1_107_converted,SRR8737281,SRR8737282
  group_25769,,Protein of unknown function (DUF2845),PGD112333,SRR8737281_00662,SRR8737282_00657
  group_25760,;hypothetical protein,hypothetical protein;topoisomerase IIProtein of unknown function (DUF2790);Protein of unknown function (DUF2790);acyl- n-acyltransferaseUncharacterized protein conserved in bacteriaProtein of unknown function DUF482;,PGD109272,SRR8737281_05540,SRR8737282_06520
  group_25759,;hypothetical protein,Protein of unknown function (DUF3309);,PGD109276,SRR8737281_05538,SRR8737282_03481
  rubA2~~~Rubredoxin2,rubA2;Rubredoxin 2,rubredoxinRubredoxin-2anaerobic nitric oxide reductase flavorubredoxinRubredoxinRubredoxin;,PGD113575,SRR8737281_00021,SRR8737282_05845
  bfr_2~~~bacterioferritin,bfr_2;bacterioferritin,bacterioferritinBacterioferritinbacterioferritinBacterioferritin (cytochrome b1)bacterioferritinFerritin-like domain;,PGD109882,SRR8737281_05955,SRR8737282_01475
  mtnB~~~probablesugaraldolase,mtnB;probable sugar aldolase,methylthioribulose-1-phosphate dehydrataseMethylthioribulose-1-phosphate dehydratasemethylthioribulose-1-phosphate dehydrataseRibulose-5-phosphate 4-epimerase and related epimerases and aldolasesmethylthioribulose-1-phosphate dehydrataseClass II Aldolase and Adducin N-terminal domain;,PGD106137,SRR8737281_02504,SRR8737282_00940
  epd_2~~~epd_1~~~epd,epd_2;epd_1;epd,D-erythrose-4-phosphate dehydrogenaseD-erythrose-4-phosphate dehydrogenaseerythrose 4-phosphate dehydrogenaseerythrose-4-phosphate dehydrogenaseGlyceraldehyde 3-phosphate dehydrogenase C-terminal domain;D-erythrose-4-phosphate dehydrogenaseD-erythrose-4-phosphate dehydrogenaseerythrose 4-phosphate dehydrogenaseTransketolaseerythrose-4-phosphate dehydrogenaseGlyceraldehyde 3-phosphate dehydrogenase C-terminal domain,PGD103840,SRR8737281_03107,SRR8737282_02473
  emrE,emrE,SMR multidrug efflux transporterMethyl viologen resistance protein Cmultidrug efflux proteinMembrane transporters of cations and cationic drugsphosphonate utilization associated putative membrane proteinSmall Multidrug Resistance protein;SMR multidrug efflux transporterMethyl viologen resistance protein Cmultidrug efflux proteinMembrane transporters of cations and cationic drugsSmall Multidrug Resistance protein,PGD112851,SRR8737281_00400,SRR8737282_00337
  purA_1~~~purA_2~~~purA,purA_1;purA_2;purA,adenylosuccinate synthetaseAdenylosuccinate synthetaseadenylosuccinate synthetaseadenylosuccinate synthaseAdenylosuccinate synthetase,PGD112747,SRR8737281_00453,SRR8737282_00390

Output

1. trim_galore directory containing adaptor-trimmed RNA-Seq files and FastQC results.
2. gene_counts directory containing:
   1. gene_set_ST.tsv: the subset of genes included in analysis.
   2. raw_counts.tsv: merged read counts per gene, scaled to the median gene length across strains.
   3. norm_counts.tsv: size factor scaled counts (normalised for library size).
   4. rpkm_counts.tsv: size factor scaled and gene length-scaled counts, expressed as reads per kilobase per million mapped reads (RPKM) (normalised for library size and gene length).
3. umap_samples directory containing UMAP visualisation of gene expression across strains.