Comparative genomics of natural fertile hybrids of Saccharomyces cerevisiae, Saccharomyces bayanus and Saccharomyces paradoxus

Natural inter-species hybrids of the genus Saccharomyces have been documented, and in some cases the hybridization gave origin to commercially useful strains. The most renowned example is that of Saccharomyces pastorianus, generated by the mating of S. cerevisiae and S. eubayanus, and widely used for pale ale beer production [1]. Other natural interspecies hybrids have been more rarely documented, probably because the low viability of their offspring strongly impact on the survival of the strain type when environmental changes are detrimentals. While natural S. cerevisiaexS. bayanus hybrids have been found, hybrids of S. cerevisiae and S. paradoxus are much more rare, as indicated by the few documented isolations [2], possibly because both the different habitat and the fact that their progeny is usually not fertile. We isolated a S. cerevisiaeS. bayanus hybrid and a S. cerevisiaeS. paradoxus hybrid from the intestine of the hornet Vespa crabro giving spores showing 100% viability and we fully sequenced the genome of each of the four meiotic segregants after sporulation. Using available compete and draft genome sequences of S. cerevisiae, S. bayanus and S. paradoxus as reference, we tested whether the two parental genomes are still physically separated after the mating by comparative genomics analysis