DNA Extraction Method Optimized for Nontuberculous Mycobacteria Long-Read Whole Genome Sequencing

Nontuberculous mycobacteria (NTM) are a major cause of pulmonary and systemic disease in at-risk populations. Gaps in knowledge about transmission patterns, evolution, and pathogenicity during infection have prompted a recent surge in genomic NTM research. Increased availability and affordability of whole genome sequencing (WGS) techniques, including the advent of Oxford Nanopore Technologies, provide new opportunities to sequence complete NTM genomes at a fraction of the previous cost. However, extracting large quantities of pure genomic DNA is particularly challenging with NTM due to their slow growth and recalcitrant cell wall. Here we report a DNA extraction protocol that is optimized for long-read WGS of NTM, yielding large quantities of highly pure DNA. Our refined method was compared to 6 other methods with variations in timing of mechanical and enzymatic digestion, quantity of matrix material, and reagents used in extraction and precipitation. We also demonstrate the ability of our optimized protocol to produce sufficient DNA to yield near-complete NTM genome assemblies using Oxford Nanopore Technologies long-read sequencing.