August 23, 2011

Lager Yeast Ancestor Found In The Forests Of Patagonia


Scientists have found a wild species of yeast that is the ancestor of that which is used to make cold-brewing ale, according to a US study published on Monday.

The yeast -- called Saccharomyces eubayanus -- was found in the deep forests of South America´s Patagonia region, living on beech trees. Scientists say the yeast was key to the invention of the crisp-tasting German beer 600 years ago.

It took five years of searching before scientists discovered, identified and named the organism. The finding is in fact the missing link to the centuries-old tale of beer-drinking, which is a $250-billion-a-year industry.

“People have been hunting for this thing for decades,” said Chris Todd Hittinger, a University of Wisconsin-Madison genetics professor and a co-author of the study, published in the Proceedings of the National Academy of Sciences (PNAS).

“And now we've found it. It is clearly the missing species. The only thing we can't say is if it also exists elsewhere (in the wild) and hasn't been found,” he said.

Researchers from Portugal, Argentina and the US teamed up to track down the elusive yeast, whose location has been a persistent mystery.

Another yeast -- Saccharomyces cerevisiae, which is responsible for warmer temperature fermentation of ale, wine and bread -- was well known. But the other was a mystery.

Geneticists have known for more than 20 years now that the yeast used to make lager, S. pastorianus, was a hybrid of two species: S. cerevisiae and some other, unidentified organism. Scientists now believe that centuries ago, S. eubayanus somehow made its way to Europe and hybridized with the domestic yeast used to brew ale. The new hybridized version could ferment at lower temperatures, needed to make lager.

Scientists from the New University of Lisbon scoured through 1,000 known species of yeast in European collections to find the mystery organism, but weren´t able to find a match. They expanded their search to international collaborators to aid in the hunt for the elusive yeast. With the aid scientist Diego Libkind of the Institute for Biodiversity and Environment Research (CONICET) in Bariloche, Argentina, they discovered a close match for the yeast in the Patagonian beech trees.

Patagonian natives used to make a fermented beverage that used yeast similar to that found in lager. That clue would prove helpful in the hunt for the elusive yeast, said Hittinger.

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

“The DNA evidence is strong,” Gavin Sherlock, a geneticist at Stanford University who has studied lager yeast but was not involved in this study, told LA Times.

Sherlock pondered how the Patagonian yeast could have traveled some 8,000 miles to Germany and end up in their lager.

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

Scientists could still yet find the yeast growing somewhere in Europe, he noted.

Another possibility is that lager yeast originated a bit later than previously thought, added Barbara Dunn, a senior research scientist who works in Sherlock's lab.

“It certainly could have existed somewhere else,” Hittinger said. “Just because somebody hasn't found it doesn't mean it doesn't exist.”

The beech forests where the lager yeast was found are cool, with an average yearly temperature of 43 to 46 degrees F, Hittinger said.

Genes that permit yeast to thrive in such chilly conditions probably provided the yeast with the ability to ferment at relatively low temperatures, conditions very similar to those prevalent in the Bavarian cellars where monks created 15th century lager, Hittinger said.

The researchers at University of Colorado compared the DNA of the 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 better improve how biofuels are produced and used, said Hittinger.

And by tinkering with yeast genes, it could also make wine and beer taste even better as well, he added.


Image 2: Orange-colored galls, such as these pictured in 2010, from the beech tree forests of Patagonia have been found to harbor the yeast that makes lager beer possible. Five hundred years ago, in the age of sail and when the trans-Atlantic trade was just beginning, the yeast somehow made its way from Patagonia to the caves and monastery cellars of Bavaria where the first lager beers were fermented. Photo: Diego Libkind, Institute for Biodiversity and Environment Research, Bariloche, Argentina


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