BWA-MEM2 — DNA Short-Read Aligner

BWA-MEM2 — DNA Short-Read Aligner

Overview

BWA-MEM2 aligns short DNA reads (Illumina, 50–250 bp) to a reference genome using the BWT-FM index. It is the standard aligner for whole-genome sequencing (WGS), whole-exome sequencing (WES), ChIP-seq, and ATAC-seq DNA alignment. BWA-MEM2 is 2× faster than the original BWA-MEM while producing identical results. It outputs SAM format with proper read group (@RG) headers required by GATK HaplotypeCaller and Picard tools. For paired-end reads, it marks proper pairs and resolves chimeric/split reads into supplementary alignments.

When to Use

• Aligning WGS or WES Illumina reads to a reference genome for variant calling (SNP, indel, SV)
• ChIP-seq or ATAC-seq DNA alignment to produce BAM files for peak calling with MACS3
• Producing GATK-compatible BAM files with @RG read group tags
• Aligning reads ≥ 50 bp; for shorter reads (< 50 bp), BWA-backtrack may be more appropriate
• Re-aligning legacy FASTQ files to an updated reference genome assembly
• Use STAR instead for RNA-seq reads that span splice junctions
• Use Bowtie2 as an alternative for local alignment or when index size must be minimized

Prerequisites

• Software: bwa-mem2 (conda or pre-compiled binary), samtools
• Reference: genome FASTA (e.g., GRCh38, hg19, mm10)
• RAM: ~28 GB for human genome index; 6–8 GB for mouse

Check before installing: The tool may already be available in the current environment (e.g., inside a pixi / conda env). Run command -v bwa-mem2 first and skip the install commands below if it returns a path. When running inside a pixi project, invoke the tool via pixi run bwa-mem2 rather than bare bwa-mem2.

# Install with conda (recommended)
conda install -c bioconda bwa-mem2 samtools

# Or download pre-compiled binary
wget https://github.com/bwa-mem2/bwa-mem2/releases/download/v2.2.1/bwa-mem2-2.2.1_x64-linux.tar.bz2
tar -jxf bwa-mem2-2.2.1_x64-linux.tar.bz2
export PATH="$PWD/bwa-mem2-2.2.1_x64-linux:$PATH"

# Verify
bwa-mem2 version
# 2.2.1

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