Long Amplicon Nanopore Sequencing for Dual-Typing RdRp and VP1 Genes of Norovirus Genogroups I and II in Wastewater

Noroviruses (NoV) are the leading cause of non-bacterial gastroenteritis across the globe with societal costs of US$60.3 billion per annum. Development of a long amplicon nanopore-based method for dual-typing the RNA-dependent RNA polymerase ( RdRp ) and major structural protein ( VP1 ) regions from a single RNA fragment could improve existing norovirus typing methods. Its application to wastewater-based epidemiology (WBE) and environmental testing could enable the discovery of novel types and improve tracking throughout the population and into aquaculture and recreational water settings. Here, we develop and optimise such a method for wastewater as the sample matrix.

Reverse transcription (RT), PCR and library pooling were optimised and a consensus-based bioinformatics pipeline was developed. Inhibitor removal and LunaScript® RT gave robust amplification of the ≈1000 bp RdRP + VP1 amplicon. Platinum™ Taq polymerase showed good sensitivity and reduced levels non-specific amplification (NSA) when compared to other polymerases. Optimised PCR annealing temperatures significantly reduced NSA (51.3% and 42.4% for GI and GII), increased yield (86.5% for GII) and increased taxa richness (57.7%) for GII. Analysis of three NoV positive faecal samples showed 100% nucleotide similarity with Sanger sequencing.

Eight GI genotypes, 11 polymerase types (p-types) and 13 combinations were detected in wastewater along with 4 GII genotypes, 4 p-types and 8 combinations; highlighting the diversity of norovirus taxa present in wastewater in England. The most common genotypes detected in clinical samples were all detected in wastewater while we also commonly detected several GI genotypes not reported in the clinical data. Application of this method into a WBE scheme, therefore, may allow for more accurate measurement of norovirus diversity within the population.