Interspecific hybridisation by digestive tract of invertebrates as a source of environmental biodiversity within the Saccharomyces cerevisiae

In order to verify whether animals can promote the formation of new yeast strains by increasing the chance of encounters between otherwise segregate spores within persistent asci, three invertebrate species representative of the marine, freshwater and terrestrial ecosystems were fed with two different diets composed of one or a combination of two strains of sporulated yeast and the egested material was analyzed for evidence. The digestive apparatus of the tested species is able to break open the asci wall (most probably by enzymatic action) produced in the species belonging to the Saccharomyces sensu stricto group without affecting the viability of the spores contained therein. The spores ejected with the fecal material have a high capacity for agglutination and, in the presence of favorable conditions, can germinate directly or conjugate to form hybrids. Hybrids between strains of the same species give rise to cultures in which the parent characteristics have new combinations. The interspecific hybrids Saccharomyces cerevisiae x Saccharomyces uvarum, although sterile, can propagate by asexual reproduction. These results support the hypothesis of horizontal transfer of genetic material between yeast species and the likelihood of hybrid formation in natural settings, and possibly shed light on the high biodiversity of yeast observed in nature.