Improved Cas9-targeted nanopore sequencing facilitates ultra-deep analysis of genomic variation

We present nanopore adapter-enriched Cas9-targeted sequencing (nAECATS), a method permitting inexpensive, ultra-deep, selective long-read sequencing of targeted regions in native, unamplified DNA. This method modifies previous Cas9-targeted sequencing approaches through the inclusion of a bead-based capture step that exploits the poly(T)₈ stretch within the R10.4.1 ligation adapter for additional purification. Testing on a 10 kb Bacteroides fragilis genomic region achieved 90% on-target yield with 51,000× coverage from a single Flongle flow cell (353-fold increase versus whole-genome sequencing). Applied to a variable-length (>20 kb) Staphylococcus aureus genomic target containing dynamic gene amplifications conferring antibiotic resistance, nAECATS achieved 46,000× coverage and 74% on-target yield, revealing 2-4 tandem amplifications at single-cell resolution. While efficiency decreased with longer fragments (up to 41 kb), substantial enrichment improvements were demonstrated. We anticipate that nAECATS ultra-deep sequencing will find broad application for a wide range of biological questions in pro- and eukaryotic (epi)genomics and microbiology.