The hybrid genomes of Saccharomyces pastorianus: A current perspective.

Saccharomyces pastorianus is a recently evolved interspecies hybrid of Saccharomyces cerevisiae and Saccharomyces eubayanus used in the production of lager-type beers and has a long-standing history with the brewing industry. At least two distinct types of lager yeasts (Groups I and II) have been identified based on chromosome content and structure. One important feature of the genomes of lager yeasts is the presence of a set of hybrid chromosomes that emerged as a result of homeologous recombination events between the parental chromosomes. The unique genetic composition of the hybrid genomes of S. pastorianus affords interesting opportunities for evolution, adaptation and survival of the hybrids. The co-expression of S. eubayanus, S. cerevisiae and hybrid gene alleles, together with gene dosage effects resulting from the presence of multiple copies of individual genes, creates a complex algorithm for gene expression, cellular biochemistry and physiology. The recent availability of genome sequences for three Group I and ten Group II lager yeast strains provides an opportunity to decipher this complex algorithm and understand how it impacts on the final fermentation product: flavoursome beer.