Ever wondered how genetically different is lager from ale beer? Researchers have now answered this query by revealing the evolution of beer yeast.
Chris Todd Hittinger of the University of Wisconsin-Madison and his team, took advantage of a newly described wild yeast species from Patagonia, Saccharomyces eubayanus, and completed and assembled a high-quality genome of S. eubayanus using next-generation sequencing.
They show two independent origin events for S. cerevisiae and S. eubanyus hybrids that brew lager beers.
The results suggested that the Saaz and Frohberg lineages (named for their area of origin) were created by at least two distinct hybridisation events between nearly identical strains of S. eubayanus with relatively more diverse ale strains of S. cerevisiae.
Hittinger said that lager yeasts did not just originate once, these hybrids were different from the start, and also changed in some predictable ways during their domestication.
They found that both the Saaz and Frohberg yeasts contained S. cerevisiae (99.57 percent identical to strain S288c) and S. eubayanus (99.55 percent identical to FM1318) genomes. They also compared the mitochondrial genomes and found S. eubayanus to be 6.6kb smaller than Frohberg yeast and 21.8kb 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.
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.
The study is published in the journal Molecular Biology and Evolution.