The prevalence of killer yeasts and double-stranded RNAs in the budding yeast Saccharomyces cerevisiae

Abstract

Killer toxins are antifungal proteins produced by many species of “killer” yeasts, including the brewer's and baker's yeast Saccharomyces cerevisiae. Screening 1270 strains of S. cerevisiae for killer toxin production found that 50% are killer yeasts, with a higher prevalence of yeasts isolated from human clinical samples and winemaking processes. Since many killer toxins are encoded by satellite double-stranded RNAs (dsRNAs) associated with mycoviruses, S. cerevisiae strains were also assayed for the presence of dsRNAs. This screen identified that 51% of strains contained dsRNAs from the mycovirus families Totiviridae and Partitiviridae, as well as satellite dsRNAs. Killer toxin production was correlated with the presence of satellite dsRNAs but not mycoviruses. However, in most killer yeasts, whole genome analysis identified the killer toxin gene KHS1 as significantly associated with killer toxin production. Most killer yeasts had unique spectrums of antifungal activities compared to canonical killer toxins, and sequence analysis identified mutations that altered their antifungal activities. The prevalence of mycoviruses and killer toxins in S. cerevisiae is important because of their known impact on yeast fitness, with implications for academic research and industrial application of this yeast species.

Molecular and biological characterization of a novel partitivirus from Talaromyces pinophilus

“…For instance, satellite dsRNAs associated with mycoviruses in the family Totiviridae encode toxins, which are secreted from ‘killer’ yeasts that harbour these dsRNA elements and kill ‘sensitive’ yeasts that do not. The killer yeast system was discovered for the first time in Saccharomyces cerevisiae , a yeast of biotechnological importance in baking, brewing and wine-making, offers an advantage to the host in competition for nutrients ( Baeza et al, 2008 ; Crabtree et al, 2023 ).…”