Murphy, H. | bioRxiv Science

bioRxiv2019

Variation in filamentous growth and response to quorum-sensing compounds in environmental isolates of Saccharomyces cerevisiae

In fungi, filamentous growth is a major developmental transition that occurs in response to environmental cues. In diploid Saccharomyces cerevisiae, it is known as pseudohyphal growth and presumed to be a foraging mechanism. Rather than normal unicellular growth, multicellular filaments composed of elongated, attached cells spread over and into surfaces. This morphogenetic switch can be induced through quorum sensing with the aromatic alcohols phenylethanol and tryptophol. Most research investigating pseudohyphal growth has been conducted in a single lab background, {Sigma}1278b. To investigate the natural variation in this phenotype and its induction, we assayed the diverse 100-genomes collection of environmental S. cerevisiae isolates. Using computational image analysis, we quantified the production of pseudohyphae and observed a large amount of variation. Unlike ecological niche, population membership was associated with pseudohyphal growth, with the West African population having the most. Surprisingly, most strains showed little or no response to exogenous phenylethanol or tryptophol. We also investigated the amount of natural genetic variation in pseudohyphal growth using a mapping population derived from a single, highly-heterozygous clinical isolate that contained as much phenotypic variation as the environmental panel. A bulk-segregant analysis uncovered five major peaks with candidate loci that have been implicated in the {Sigma}1278b background. Our results indicate that the filamentous growth response is a generalized, highly variable phenotype in natural populations, while response to quorum sensing molecules is surprisingly rare. These findings highlight the importance of coupling studies in tractable lab strains with natural isolates in order to understand the relevance and distribution of well-studied traits.

genetics↗

bioRxiv2017

Biofilm formation and toxin production provide a fitness advantage in mixed colonies of natural yeast isolates

Microbes exist in complex communities and can engage in social interactions ranging from cooperation to warfare. Biofilms are structured, cooperative microbial communities; they are pervasive and ancient, representing the first fossilized life. Like all cooperative communities, biofilms are susceptible to invasion by selfish individuals who benefit from cooperation, but do not contribute. The ubiquity of biofilms therefore poses a challenge to evolutionary theory. One hypothesis for biofilm stability is spatial structure: patches of related cooperative cells are able to outcompete unrelated cells. These dynamics have been explored computationally and in bacterial systems; however, their relevance to eukaryotic microbes remains an open question. Here, we investigate the interactions of environmental yeast isolates with different social phenotypes. Our results show that biofilm strains spatially exclude non-biofilm strains, and that biofilm spatial structure confers a consistent and robust fitness advantage in direct competition. We also find that biofilms protect against killer toxin, a warfare phenotype. During biofilm formation, cells are susceptible to toxin from nearby competitors; however, increased spatial use by biofilms provides an escape from toxin-producers. Our results suggest that yeast biofilms represent a competitive strategy, and that principles elucidated for the evolution and stability of bacterial biofilms may apply to eukaryotes.

evolutionary biology↗