Identification and Molecular Characterization of Novel Mycoviruses in Saccharomyces and non-Saccharomyces Yeasts of Oenological Interest

Wine yeasts can be natural hosts for dsRNA, ssRNA viruses and retrotransposon elements. In this study, high-throughput RNA sequencing combined to bioinformatic analyses unveiled the viriome associated to 16 Saccharomyces cerevisiae and 8 non-Saccharomyces strains of oenological interest. Results showed the presence of eight viruses from four different families, two of which--Partitiviridae and Mitoviridae--not reported before in yeasts, as well as two ORFan contigs of viral origin. According to phylogenetic analysis, four new putative mycoviruses distributed in Totivirus, Cryspovirus and Mitovirus genera were identified. The majority of commercial S. cerevisiae strains were confirmed to be host for helper L-A type totiviruses and satellite M dsRNAs associated to killer phenotype, both in single and mixed infections with L-BC totiviruses, and two viral sequences belonging to a new cryspovirus putative species discovered here for the first time. Moreover, single infection by a narnavirus 20S-related sequence was also found in one S. cerevisiae strain. Considering the non-Saccharomyces yeasts, Starmerella bacillaris hosted four RNAs of viral origin-- two clustering in Totivirus and Mitovirus genera, and two ORFans with putative satellite behaviour. This study confirmed infection of wine yeasts by viruses associated to useful technological characteristics and demonstrated the presence of complex mixed infections with unpredictable biological effects.