Abstract

Saccharomyces cerevisiae is one of the best studied eukaryotic model organisms. It can alternate between haploid and diploid phases, with lack of nutrients favoring a switch to the haploid phase through a mechanism called sporulation. During sporulation, a single diploid cell generates four haploid daughter cells -a tetrad- which are tightly enclosed within a structure called the ascus. Confinement within the ascus is thought to enforce mating between products of the same meiotic division, minimizing outcrossing in this stage of the life cycle. Therefore, outbreeding has been commonly considered extremely rare in nature. Recent studies, however, have begun to challenge this view by uncovering a surprising ecological niche for the outbreeding of wild yeast: the guts of wasps. Yeast outbreeding in this environment likely involves an interaction between the physicochemical environment of the gut and the biological response of the cells. Preliminary results indicate that ascus breakage results from the combination of physical stresses and enzymatic digestion factors. Mixing due to movement at the gut-level can then promote the formation of multi-strain aggregates and outbreeding. Understanding the natural mechanisms leading to yeast outbreeding in nature will lead us to a better understanding of the S. cerevisiae evolution and adaptation capability. This project is a part of a HFSP grant entitled “The aphrodisiac gut”, in collaboration with research groups specialized in Chemistry from University of Sydney, in Biology from University of Turin and Mathematics from Boston University.