Next-generation sequencing analysis of lager brewing yeast strains reveals the evolutionary history of interspecies hybridization.

The lager beer yeast Saccharomyces pastorianus is considered an allopolyploid hybrid species between S. cerevisiae and S. eubayanus. Many S. pastorianus strains have been isolated and classified into two groups according to geographical origin, but this classification remains controversial. Hybridization analyses and partial PCR-based sequence data have indicated a separate origin of these two groups, whereas a recent intertranslocation analysis suggested a single origin. To clarify the evolutionary history of this species, we analysed 10 S. pastorianus strains and the S. eubayanus type strain as a likely parent by Illumina next-generation sequencing. In addition to assembling the genomes of five of the strains, we obtained information on interchromosomal translocation, ploidy, and single-nucleotide variants (SNVs). Collectively, these results indicated that the two groups of strains share S. cerevisiae haploid chromosomes. We therefore conclude that both groups of S. pastorianus strains share at least one interspecific hybridization event and originated from a common parental species and that differences in ploidy and SNVs between the groups can be explained by chromosomal deletion or loss of heterozygosity.