Sequencing, Assembling, and Finishing Complete Bacteriophage Genomes

Next-generation DNA sequencing (NGS) technologies have made generating genomic sequence for organisms of interest affordable and commonplace. However, NGS platforms and analysis software are generally tuned to be used on large and complex genomes or metagenomic samples. Determining the complete genome sequence of a single bacteriophage requires a somewhat different perspective, workflow, and sensitivity to the nature of phages. Because phage genomes consist of mostly coding regions (see Pope/Jacobs-Sera chapter), a very high standard should be adopted when completing these genomes so that the subsequent steps of annotation and analysis are not sabotaged by sequencing errors. While read quality and assembly algorithms have continued to improve, achieving this standard still requires a significant amount of human oversight and expertise. This chapter describes our workflow for sequencing, assembling, and finishing phage genomes to a high standard by the NGS platforms Illumina, Ion Torrent, and 454.

Enly: Improving Draft Genomes through Reads Recycling

The reconstruction of the complete genome sequence of an organism is an important point for comparative, functional and evolutionary genomics. Nevertheless, overcoming the problems encountered while completing the sequence of an entire genome can still be demanding in terms of time and resources. We have developed Enly, a simple tool based on the iterative mapping of sequence reads at contig edges, capable to extend the genomic contigs deriving from high-throughput sequencing, especially those deriving by Newbler-like assemblies. Testing it on a set of de novo draft genomes led to the closure of up to 20% of the gaps originally present. Enly is cross-platform and most of the steps of its pipeline are parallelizable, making easy and fast to improve a draft genome resulting from a de novo assembly.