Metagenomic sequencing is a promising method to determine the virus diversity in environmental samples such as sewage or shellfish. However, to identify the short RNA genomes of human enteric viruses among the large diversity of nucleic acids present in such complex matrices, method optimization is still needed. This work presents methodological developments focused on norovirus, a small ssRNA non-enveloped virus known as the major cause of human gastroenteritis worldwide and frequently present in human excreta and sewage. Different elution protocols were applied and Illumina MiSeq technology were used to study norovirus diversity. A double approach, agnostic deep sequencing and a capture-based approach (VirCapSeq-VERT) was used to identify norovirus in environmental samples. Family-specific viral contigs were classified and sorted by SLIM and final norovirus contigs were genotyped using the online Norovirus genotyping tool v2.0. From sewage samples, 14 norovirus genogroup I sequences were identified of which six were complete genomes. For norovirus genogroup II, nine sequences were identified and three of them comprised more than half of the genome. In oyster samples bioaccumulated with these sewage samples, only the use of an enrichment step during library preparation allowed successful identification of nine different sequences of norovirus genogroup I and four for genogroup II (>500 bp). This study demonstrates the importance of method development to increase virus recovery, and the interest of a capture-based approach to be able to identify viruses present at low concentrations.

Targeted sequence capture is a promising technology which helps reduce costs for sequencing and genotyping numerous genomic regions in large sets of individuals. Bait sequences are designed to capture specific alleles previously discovered in parents or reference populations. We studied a set of 135 RILs originating from a cross between an emmer cultivar (Dic2) and a recent durum elite cultivar (Silur). Six thousand sequence baits were designed to target Dic2 vs. Silur polymorphisms discovered in a previous RNAseq study. These baits were exposed to genomic DNA of the RIL population. Eighty percent of the targeted SNPs were recovered, 65% of which were of high quality and coverage. The final high density genetic map consisted of more than 3,000 markers, whose genetic and physical mapping were consistent with those obtained with large arrays.

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Bivalve molluscan shellfish (BMS) contamination with gastroenteritis viruses such as norovirus (NoV) is recognized as a significant public health risk worldwide. These foodborne epidemics are characterized by very low viral concentrations in the implicated foods, and by diverse viruses or multiple NoV strains originating from human sewage, resulting in different strains (co‐)infecting the consumers. Next‐generation sequencing (NGS) offers promising means to describe the diversity of strains present in BMS or to retrace transmission chains in outbreak settings, but their sensitivity and reproducibility remained to be assessed for this application. In this work, we evaluated the ability of three promising NGS methods to sequence diverse NoV in environmental or food BMS and human stool samples. Using laboratory‐prepared samples of known NoV composition, we evaluated the sensitivity, reproducibility, repeatability and selectivity of metabarcoding, capture‐based metagenomics and long amplicon sequencing, considering representative NoV strains from genogroup I and II, and the impact of the BMS matrix. The metabarcoding, with separate amplification of polymerase and capsid gene segments followed by Illumina sequencing, was the most sensitive method. It was applied to a selection of 212 BMS samples collected through the European Commission’s NoV baseline survey (BLS), demonstrating a high diversity of NoV sequences found in the BMS which reflect the diversity of NoV strains circulating in the European human population. Besides, a capture‐based metagenomics with enrichment of vertebrate viruses was applied on 20 of these BLS samples as well as 20 BMS linked to outbreaks and 10 related human stool samples. In BMS, it yielded NoV sequences compatible with the genomes identified in stool samples, but they were too short to allow definitive confirmation of the infection source. The present report describes NGS methods, including the bioinformatic pipelines, applicable to molecular epidemiology of NoV in BMS, their current limitations and expected outcomes.

Since the beginning of the Coronavirus Disease-19 (COVID-19) pandemic, multiple Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) mutations have been reported and led to the emergence of variants of concern (VOC) with increased transmissibility, virulence or immune escape. In parallel, the observation of viral fecal shedding led to the quantification of SARS-CoV-2 genomes in wastewater, providing information about the dynamics of SARS-CoV-2 infections within a population including symptomatic and asymptomatic individuals. Here, we aimed to adapt a sequencing technique initially designed for clinical samples to apply it to the challenging and mixed wastewater matrix, and hence identify the circulation of VOC at the community level. Composite raw sewage sampled over 24 h in two wastewater-treatment plants (WWTPs) from a city in western France were collected weekly and SARS-CoV-2 quantified by RT-PCR. Samples collected between October 2020 and May 2021 were submitted to whole-genome sequencing (WGS) using the primers and protocol published by the ARTIC Network and a MinION Mk1C sequencer (Oxford Nanopore Technologies, Oxford, United Kingdom). The protocol was adapted to allow near-full genome coverage from sewage samples, starting from ∼5% to reach ∼90% at depth 30. This enabled us to detect multiple single-nucleotide variant (SNV) and assess the circulation of the SARS-CoV-2 VOC Alpha, Beta, Gamma, and Delta. Retrospective analysis of sewage samples shed light on the emergence of the Alpha VOC with detection of first co-occurring signature mutations in mid-November 2020 to reach predominance of this variant in early February 2021. In parallel, a mutation-specific qRT-PCR assay confirmed the spread of the Alpha VOC but detected it later than WGS. Altogether, these data show that SARS-CoV-2 sequencing in sewage can be used for early detection of an emerging VOC in a population and confirm its ability to track shifts in variant predominance.