Assembling the perfect bacterial genome using Oxford Nanopore and Illumina sequencing

A perfect bacterial genome assembly is one where the assembled sequence is an exact match for the organism's genome-each replicon sequence is complete and contains no errors. While this has been difficult to achieve in the past, improvements in long-read sequencing, assemblers, and polishers have brought perfect assemblies within reach. Here, we describe our recommended approach for assembling a bacterial genome to perfection using a combination of Oxford Nanopore Technologies long reads and Illumina short reads: Trycycler long-read assembly, Medaka long-read polishing, Polypolish short-read polishing, followed by other short-read polishing tools and manual curation. We also discuss potential pitfalls one might encounter when assembling challenging genomes, and we provide an online tutorial with sample data (github.com/rrwick/perfect-bacterial-genome-tutorial).

Automated summary

A perfect bacterial genome assembly requires improved long-read sequencing, assemblers, and polishers. By combining Oxford Nanopore Technologies long reads and Illumina short reads, we suggest using Trycycler long-read assembly, Medaka long-read polishing, Polypolish short-read polishing, and additional short-read polishing tools and manual curation. We also discuss potential challenges and provide an online tutorial for reference.