Creation of Lager Strains with Unique Genomic Structure

Lager beer is produced Saccharomyces pastorianus, which is a natural allotetraploid hybrid between Saccharomyces cerevisiae and Saccharomyces eubayanus. Lager strains are classified into two major groups based largely on genomic composition, Group I strains having a allotriploid composition and Group II being allotetraploid. A lack of phenotypic diversity in commercial lager strains has led to the reconstitution of de novo allotetraploid lager strains by hybridization of S. cerevisiae and S. eubayanus strains. Such strategies rely on the hybridization of wild S. eubayanus isolates which carry traits which are not ideal for commercial lager beer production. Using a different breeding strategy, we have created de novo lager hybrids which contain the domesticated S. eubayanus subgenome from an industrial S. pastorianus strain by hybridizing a diploid meiotic segregant to a variety of S. cerevisiae ale strains. By applying proper selection, we have isolated five such de novo hybrids which have fermentation characteristics similar to those of prototypical commercial lager strains but display phenotypic variation leading to the production of unique volatile profiles suitable for lager beer. Genomic analysis of these de novo lager hybrids identified novel genome structures where the hybrids display a unique allotetraploid genome carrying three copies of the S. cerevisiae genome and one copy of the S. eubayanus genome. Most importantly, these hybrids do not possess any of the negative traits that are common with de novo lager strains made by other breeding approaches resulting in novel lager strains which are immediately suitable for industrial lager beer production.