As any beer snob worth their salt will tell you that a good brew depends largely on the quality of the yeast – but what exactly do we know about the evolution of the fungal organisms frequently used as ingredients in the various ales and lagers enjoyed the world over?
Chris Todd Hittinger, a professor in the University of Wisconsin-Madison’s genetics laboratory, graduate student Emily Clare Baker, and their colleagues set out to discover the origins of hybrid yeast strains used to create lagers, using cutting-edge sequencing techniques in order to complete and assemble a high-quality genome of a newly-described species found in Patagonia.
This new wild species, Saccharomyces eubayanus, was compared to the domesticated hybrids used to brew larger-style brews, allowing researchers to study the complete genomes of both parental yeast species (S. cerevisiae and S. eubayanus) used to craft these popular beverages for the first time. The findings appear in the journal Molecular Biology and Evolution.
Lager hybrids had at least two independent lineages
Oddly enough, Hittinger and Baker’s research revealed that there are two independent origin events for the S. cerevisiae and S. eubanyus hybrids used to brew lager beers, and that despite significant genetic differences between the two different types of yeast, there were at least two distinct hybridization events involving strains of these two different organisms.
Identified by the authors as the Saaz and Frohberg lineages (based on their area of origin), the two evolutionary origins involved nearly identical strains of S. eubayanus and relatively more diverse ale strains of S. cerevisiae, the authors explained in a press release. The study clarifies the origins of these two major hybrid yeast origins, and could direct future research focused on the domestication of lager yeasts.
In addition to discovering that hybrid lager yeasts had originated at least twice, Hittinger told redOrbit that he and Baker discovered that “the domesticated S. eubayanus subgenomes in the hybrids experienced a dramatic increase in their rate of evolution (specifically protein versus neutral changes), as is frequently observed in domesticated plants and animals.”
“There were two major hypotheses about the origins of the Saaz and Frohberg groups, [and] there was some prior support for each, so both models were plausible,” he added via email. “I was surprised at how clear the results were with over 10x more differentiation between the S. cerevisiae subgenomes.” The findings, Hittinger said, reveal “how little we still know about natural Saccharomyces diversity,” and since only a subset of the species have been utilized by industry, “there is a lot of potential to create novel, custom brewing or biofuel strains.”
(Image credit: Thinkstock)
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