Cold-adapted yeast a native of Patagonia

WHILST lager beer is one of the most popular drinks in the world, there are a few things about it that experts don’t know about, such as the history of the cold-adapted yeast, Saccharomyces eubayanus.

The wandering parent of hybrid lager yeast discovered in 2011, S. eubayanus has been confirmed to be a native of Patagonia. An analysis of the yeast’s genetic sequence revealed its closest affinity to one of two highly diverse Patagonian populations, confirming it was the cold-loving microbe that, 500 years ago, found its way to the caves and monastery cellars of Bavaria where lager beer was first concocted.

Patagonian galls, above,  harbor the cold-adapted yeast Saccharomyces eubayanus, a parent of the hybrid yeast used to make lager or cold-brewed beer. (Photo courtesy of Diego Libkind, Institute for Biodiversity and Environment Research, Bariloche, Argentina)

Prof Hittinger’s colleague, Diego Libkind of the Institute for Biodiversity and Environment Research in Bariloche, Argentina, and a co-author of the new study, has conducted extensive field surveys, combing the Patagonian landscape where the cold-adapted yeast that he discovered seems to occur at a very high rate.

Despite their prevalence in Patagonia, they are no longer exclusive to South America. Prof Hittinger and his group also discovered S. eubayanus, with genetic hallmarks of the Patagonian strains, in a single North American location: Indian Mound Park, near Sheboygan, Wisconsin. It is the first time the microbe has been found in nature in North America, or indeed outside of Patagonia. Found by UW-Madison undergraduate student Kayla Sylvester, a member of Prof Hittinger’s group, the yeast occurs only at a very low frequency and was likely accidentally introduced, just as an ancestor found its way to Europe and kick-started the production of cold-brewed lager beer hundreds of years ago.

“If I had to bet, I’d lay money on ski bums or migrating birds” as the agents responsible for transporting the microbe to Wisconsin, says Prof Hittinger. “What we think is happening is that well-established, genetically diverse populations are sending migrants around the world. Generally, they’re not successful, but occasionally they are.”

Thankfully, S. eubayanus met a match in Europe to form the lager hybrid. The world’s 1,500 or so described yeasts are masters of what scientists call reticulate evolution, the ability to add traits by hybridising or otherwise combining different species. Although rare in nature, the huge populations and strong selection that exist in industrial fermentations allow even rare hybrids to be recovered, if they are favoured.

By exploring yeasts’ native habitat and looking to see where else in the world they have turned up, scientists may unlock secrets of yeast genetics and hybridisation with enormous economic benefit.

“Yeasts are important for fermenting processes and biotechnology,” notes genetics graduate student David Peris, also of UW-Madison and a co-author of the new study. “The value of studying diversity is that you can pull out genes or strains that can be used for a particular industrial process.”

Their primary job in industrial fermentation settings is to break down sugars, converting them to alcohol. The grail of modern industrial fermentation research is perfecting fermentation processes for things like biofuels. Four of the seven known natural Saccharomyces species of yeast are now known to be involved in industrial processes, at least as interspecies hybrids.

“The idea is to tap into biodiversity and find the strains that ferment better and those strains, or their genes, can be plugged into industrial processes,” Prof Hittinger says.

Brewers and winemakers, he notes, have unwittingly selected for hybrids. The tools of modern biotechnology, he explains, can potentially refine industrial fermentation by mixing and matching genes that lead to a better conversion of sugar to alcohol.

The new study, which appears in Molecular Ecology was supported by a grant from the National Science Foundation and was funded in part by the Department of Energy-funded Great Lakes Bioenergy Research Centre.