Scent of a killer: How could killer yeast boost its dispersal?

Abstract

Vector‐borne parasites often manipulate hosts to attract uninfected vectors. For example, parasites causing malaria alter host odor to attract mosquitoes. Here, we discuss the ecology and evolution of fruit‐colonizing yeast in a tripartite symbiosis—the so‐called “killer yeast” system. “Killer yeast” consists of Saccharomyces cerevisiae yeast hosting two double‐stranded RNA viruses (M satellite dsRNAs, L‐A dsRNA helper virus). When both dsRNA viruses occur in a yeast cell, the yeast converts to lethal toxin‑producing “killer yeast” phenotype that kills uninfected yeasts. Yeasts on ephemeral fruits attract insect vectors to colonize new habitats. As the viruses have no extracellular stage, they depend on the same insect vectors as yeast for their dispersal. Viruses also benefit from yeast dispersal as this promotes yeast to reproduce sexually, which is how viruses can transmit to uninfected yeast strains. We tested whether insect vectors are more attracted to killer yeasts than to non‑killer yeasts. In our field experiment, we found that killer yeasts were more attractive to Drosophila than non‐killer yeasts. This suggests that vectors foraging on yeast are more likely to transmit yeast with a killer phenotype, allowing the viruses to colonize those uninfected yeast strains that engage in sexual reproduction with the killer yeast. Beyond insights into the basic ecology of the killer yeast system, our results suggest that viruses could increase transmission success by manipulating the insect vectors of their host.

Infection by dsRNA viruses is associated with enhanced sporulation efficiency in Saccharomyces cerevisiae

“…cerevisiae are known for encoding toxin production as an interference competition mechanism. Recently, Buser et al (2021) found that yeast hosting dsRNA viruses were more attractive to Drosophila simulans , a Drosophilid responsible for yeast dispersal (Buser et al, 2014). Surviving dispersal via gut passage requires sporulation.…”

“…Strains that are more attractive would therefore have higher sporulation rates as insect vectors disperse them more frequently. It was recently shown that killer yeasts are generally more attractive than non-killers (Buser et al, 2021). An alternative explanation for the higher sporulation rate in killers could therefore be that it is an adaptive trait making up for their higher attraction to insect vectors.…”

Impact of intraspecific variation in insect microbiomes on host phenotype and evolution

“…This interaction influences the feeding of Drosophila spp. and promotes the dispersal of killer yeasts to new fruits [ 56 ].…”