The molecular characterization of new types of Saccharomyces cerevisiae×S. kudriavzevii hybrid yeasts unveils a high genetic diversity.

New double- and triple-hybrid Saccharomyces yeasts were characterized using PCR-restriction fragment length polymorphism of 35 nuclear genes, located on different chromosome arms, and the sequencing of one nuclear and one mitochondrial gene. Most of these new hybrids were originally isolated from fermentations; however, two of them correspond to clinical and dietary supplement isolates. This is the first time that the presence of double-hybrid S. cerevisiae×S. kudriavzevii in non-fermentative substrates has been reported and investigated. Phylogenetic analysis of the MET6 nuclear gene confirmed the double or triple parental origin of the new hybrids. Restriction analysis of gene regions in these hybrids revealed a high diversity of genome types. From these molecular characterizations, a reduction of the S. kudriavzevii fraction of the hybrid genomes is observed in most hybrids. Mitochondrial inheritance in hybrids was deduced from the analysis of mitochondrial COX2 gene sequences, which showed that most hybrids received the mitochondrial genome from the S. kudriavzevii parent. However, two strains inherited a S. cerevisiae COX2, being the first report of S. cerevisiae×S. kudriavzevii hybrids with S. cerevisiae mitochondrial genomes. These two strains are those showing a higher S. kudriavzevii nuclear genome reduction, especially in the wine hybrid AMH. This may be due to the release of selective pressures acting on the other hybrids to maintain kudriavzevii mitochondria-interacting genes.