JASPER: a fast genome polishing tool that improves accuracy and creates population-specific reference genomes

Advances in long-read sequencing technologies have dramatically improved the contiguity and completeness of genome assemblies. Using the latest nanopore-based sequencers, we can generate enough data for the assembly of a human genome from a single flow cell. With the long-read data from these sequences, we can now routinely produce de novo genome assemblies in which half or more of a genome is contained in megabase-scale contigs. Assemblies produced from nanopore data alone, though, have relatively high error rates and can benefit from a process called polishing, in which more-accurate reads are used to correct errors in the consensus sequence. In this manuscript, we present a novel tool for genome polishing called JASPER (Jellyfish-based Assembly Sequence Polisher for Error Reduction). In contrast to other polishing methods, JASPER gains efficiency by avoiding the alignment of reads to the assembly. Instead, JASPER uses a database of k-mer counts that it creates from the reads to detect and correct errors in the consensus. In addition to its use for polishing genomes, JASPER can also create population-specific genomes using an existing reference genome along with sequencing reads from multiple individuals from the population of interest. In this mode, JASPER alters the reference genome so that it contains variants that are common in the target population. In our experiments, we show that after creating a Japanese-specific reference genome, we observed a 27% reduction in homozygous variant calls using whole-genome sequencing reads from an individual from Tokyo.