The Evolution of Beer

From Austrian monks to American craft brewers, beer geeks are everywhere. But making a good beer not only depends on the best ingredients, but also the best yeast. The beer world is divided into ales and lagers. Lager yeasts are hybrid strains, made of two different yeast species, Saccharomyces cerevisiae and S. eubayanus (discovered in 2011). In a new study in the journal Molecular Biology and Evolution , graduate student Emily Clare Baker, corresponding author Baker et al. (2015) studied the complete genomes of both parental yeast species contributing to lager beer. They proved that two independent origin events occurred for S. cerevisiae and S. eubanyus hybrids found in lager beers. Lager beer making has placed yeast on similar evolutionary trajectories multiple times. “Lager yeasts did not just originate once. This unlikely marriage between two species, genetically as different from one another as humans and birds, happened at least twice. Although these hybrids were different from the start, they also changed in some predictable ways during their domestication,” said Hittinger. The blueprint of the powerhouses of the yeast cell, called mitochondrial genome sequences, proved that S. eubayanus served as the main donor of mtDNA for lager yeasts of Frohberg lineage. They also found that both the Saaz and Frohberg yeasts contained S. cerevisiae (99.57% identical to strain S288c) and S. eubayanus (99.55% identical to FM1318) genomes. They also compared the mitochondrial genomes and found S. eubayanus to be 6.6 kb smaller than Frohberg yeast and 21.8 kb smaller than S. cerevisiae . In addition, since being adapted for beer making, the S. eubayanus genomes have experienced increased rates of evolution, including in some genes involved in metabolism. Some metabolism genes, especially those involved in fermentation and sugar metabolism, may have been shaped by domestication in brewing. In particular, the authors suggest that many evolutionary changes may have reduced the function of the Adr1 protein, which activates an alcohol dehydrogenase that consumes alcohol, rather than producing it. The findings have now clarified the origins of the major lineages of the hybrid yeasts used to brew lagers, and will provide a roadmap for future research in the domestication of lager yeasts.