Recovery of small plasmid sequences via Oxford Nanopore sequencing

Oxford Nanopore Technologies (ONT) sequencing platforms currently offer two approaches to whole-genome native-DNA library preparation: ligation and rapid. In this study, we compared these two approaches for bacterial whole-genome sequencing, with a specific aim of assessing their ability to recover small plasmid sequences. To do so, we sequenced DNA from seven plasmid-rich bacterial isolates in three different ways: ONT ligation, ONT rapid and Illumina. Using the Illumina read depths to approximate true plasmid abundance, we found that small plasmids (<20 kbp) were underrepresented in ONT ligation read sets (by a mean factor of similar to 4) but were not underrepresented in ONT rapid read sets. This effect correlated with plasmid size, with the smallest plasmids being the most underrepresented in ONT ligation read sets. We also found lower rates of chimaeric reads in the rapid read sets relative to ligation read sets. These results show that when small plasmid recovery is important, ONT rapid library preparations are preferable to ligation-based protocols.

Automated summary

This study compared the ligation and rapid approaches for bacterial whole-genome sequencing by Oxford Nanopore Technologies, finding that the rapid library preparation method is preferable for recovering small plasmid sequences. Sequencing DNA from seven plasmid-rich bacterial isolates using Illumina as a reference, it was observed that small plasmids were underrepresented in ligation read sets but not in rapid read sets. The results also showed lower rates of chimaeric reads in the rapid read sets compared to ligation read sets.