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takyon writes:

Genes behind lager yeast's cold- and sugar-loving success revealed

Lager beer is cold, crisp, dry — and worth about half a trillion dollars worldwide. Behind the world's most popular alcoholic beverage is a yeast adapted to the cold, and hungry for the sugars it will transform into bubbles and booze. That yeast is a hybrid, an amalgamation of the domesticated baker's yeast Saccharomyces cerevisiae and a recently discovered wild species, Saccharomyces eubayanus. Hundreds of years ago, the two species combined their strengths into a cold-fermenting strain that readily produces the crisp, light taste that came to dominate the beer market in the centuries that followed.

In a pair of new papers, University of Wisconsin–Madison Professor of Genetics Chris Todd Hittinger, his graduate student EmilyClare Baker and others show how modern lager yeast adopted the cold-loving and sugar-hungry traits essential to their success.

In one paper, to be published Feb. 1 in Science Advances, the team demonstrates that when the cold-loving S. eubayanus donated its mitochondria — the power-generating portion of the cell — to the new hybrid, it conferred cold tolerance on the strain. Today, all industrial lager strains retain the S. eubayanus mitochondria and ferment at cold temps.

In a second paper, Baker and Hittinger investigated the ability of S. eubayanus to ferment all the sugars in wort, the barley malt extract that ferments into beer. Most strains of S. eubayanus cannot ferment maltotriose, the second-most common sugar in wort. But the researchers were able to evolve a brand-new protein capable of transporting maltotriose into the cell, revealing a potential path to more aggressive fermentation of all available sugars, a key trait in producing a dry, crisp beer. The paper was published on the pre-print server bioRxiv ahead of publication in the journal PLOS Genetics.

Mitochondrial DNA and temperature tolerance in lager yeasts (open, DOI: 10.1126/sciadv.aav1869) (DX)

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