Geneticists find lager’s missing link in Patagonia

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Larryh86GT

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http://www.buffalonews.com/life/article578785.ece

How did lager beer come to be? After pondering the question for decades, scientists have found that an elusive species of yeast isolated in the forests of Argentina was key to the invention of the crisp-tasting German beer 600 years ago.

It took a five-year search around the world before the scientific team discovered, identified and named the organism, a species of wild yeast called Saccharomyces eubayanus that lives on beech trees.

“We knew it had to be out there somewhere,” said Chris Todd Hittinger, an evolutionary geneticist at the University of Wisconsin-Madison and a co-author of the report published in the Proceedings of the National Academies of Sciences.

Their best bet is that centuries in the past, S. eubayanus somehow found its way to Europe and hybridized with the domestic yeast used to brew ale, creating an organism that can ferment at the lower temperatures used to make lager.

Geneticists have known since the 1980s that the yeast brewers use to make lager, S. pastorianus, was a hybrid of two yeast species: S. cerevisiae— used to make ales, wine and bread—and some other, unidentified organism.

Searching through collections of wild yeasts from Europe, researchers —including Hittinger and his collaborators— tried to identify lager’s missing link but again and again were stumped. “There were a few candidates, but none fit particularly well,” Hittinger said.

So he and his colleagues began “sampling more systematically,” collecting soil and bark, sap and abnormal growths called galls from trees on five different continents.

Team member Diego Libkind, of the Institute for Biodiversity and Environment Research in Bariloche, Argentina, found S. eubayanus in galls on southern beech trees in Patagonia. The galls were particularly rich in sugar, which yeast like to colonize and consume.

Patagonian natives used to make a fermented beverage from the galls— a definite clue that the scientists were on the right track, Hittinger said.

When the team brought the yeast to a lab at the University of Colorado and analyzed its genome, they discovered that it was 99.5 percent identical to the non-ale portion of the S. pastorianus genome, suggesting it was indeed lager yeast’s long-lost ancestor.

“The DNA evidence is strong,” said Gavin Sherlock, a geneticist at Stanford University who has studied lager yeast but was not involved in this study. But Sherlock wondered how S. eubayanus could have traveled the nearly 8,000 miles from Argentina to Germany.

“We all know that in 1492, Columbus sailed the ocean blue,” he said. “Lager was invented in the 1400s. It’s not really clear how that progenitor would have gotten from South America to Europe.”

The beech forests where the team found S. eubayanus are cool, with an average year-round temperature of 43 to 46 degrees Fahrenheit, said Hittinger. Genes that permit the yeast to thrive in such a chilly environment probably provided S. pastorianus’ ability to ferment at relatively lowtemperatures— conditions not too terribly different from those prevalent in the Bavarian cellars where monks created the golden brew back in the 15th century.

The researchers compared the DNA of the wild Patagonian yeast with that of lager yeast used in breweries to see what changes had evolved over the years. They found changes in genes that regulate sugar and sulfite metabolism, processes that contribute to the fermentation and preservation of beer. Scientists could exploit such knowledge to improve biofuels, he said.

And of course, tinkering with yeast genes might make wine or beer taste better, too, said Hittinger, who is “a lager man.” Co-author Mark Johnston, a molecular biologist at the University of Colorado School of Medicine, prefers ales.
 
Very interesting article that I missed before. Thanks for sharing and reviving!
 

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