Laboratory evolution of aSaccharomyces cerevisiaexS. eubayanushybrid under simulated lager-brewing conditions: genetic diversity and phenotypic convergence

Abstract

AbstractSaccharomyces pastorianuslager-brewing yeasts are domesticated hybrids ofS. cerevisiaexS. eubayanusthat display extensive inter-strain chromosome copy number variation and chromosomal recombinations. It is unclear to what extent such genome rearrangements are intrinsic to the domestication of hybrid brewing yeasts and whether they contribute to their industrial performance. Here, an allodiploid laboratory hybrid ofS. cerevisiaeandS. eubayanuswas evolved for up to 418 generations on wort under simulated lager-brewing conditions in six independent sequential batch bioreactors. Characterization of 55 single-cell isolates from the evolved cultures showed large phenotypic diversity and whole-genome sequencing revealed a large array of mutations. Frequent loss of heterozygosity involved diverse, strain-specific chromosomal translocations, which differed from those observed in domesticated, aneuploidS. pastorianusbrewing strains. In contrast to the extensive aneuploidy of domesticatedS. pastorianusstrains, the evolved isolates only showed limited (segmental) aneuploidy. Specific mutations could be linked to calcium-dependent flocculation, loss of maltotriose utilisation and loss of mitochondrial activity, three industrially relevant traits that also occur in domesticatedS. pastorianusstrains. This study indicates that fast acquisition of extensive aneuploidy is not required for genetic adaptation ofS. cerevisiaexS. eubayanushybrids to brewing environments. In addition, this work demonstrates that, consistent with the diversity of brewing strains for maltotriose utilization, domestication under brewing conditions can result in loss of this industrially relevant trait. These observations have important implications for the design of strategies to improve industrial performance of novel laboratory-made hybrids.