Yeast studies never grabbed the academic spotlight like more charismatic species, say, bacteria or green algae. But a new discovery is rocking this placid pantry of academe.
Microbiologists have identified the wild roots of the yeast that allows humans to brew lagers.
Lager isn't just another word for beer (although it is the most popular commercial brew); it refers to a specific type of beer brewed at lower temperatures than the ales popular from the time of Amenhotep to the age of Budweiser. Lagers require a particularly hardy strain of yeast, a hybrid of the ancient strain of brewer's yeast and some other wild strain that apparently wasn't in the suds arsenal until brewmasters latched onto it in 15th-century Bavaria.
The search for that wild strain led to a sort of globe-spanning, half-decade-long eukaryotic treasure hunt, according to a team of eight researchers writing in the latest edition of the Proceedings of the National Academy of Sciences. The pursuers eventually treed their quarry — literally — in the beech forests of Patagonia.
The yeast in question came from galls — outgrowths on plants cased by bugs or infections, kind of like plant pimples — found on southern beeches in the far south of Argentina. The researchers had two breaks in the case — they knew that brewer's yeast was strongly associated with oak trees and their kin, and their lead author, Diego Libkind, works at Argentina's Institute for Biodiversity and Environment Research. (Plus, as team member and evolutionary geneticist Chris Todd Hittinger of the University of Wisconsin-Madison told the Los Angeles Times in its fine write-up of the discovery, the locals already made a potent potable from the galls.)
"Beech galls are very rich in simple sugars," Hittinger told his alma mater. "It's a sugar-rich habitat that yeast seems to love." The more or less free-ranging yeast microbes found the galls a congenial home, so when humans made the drink from the galls, they had the yeast and the sugars already in place, which are the building blocks of booze.
Folks better with history than test tubes might ask how a New World yeast found its way into an almost pre-Colombian Old World brew, but the researchers believe nascent transatlantic trade and a hardy yeast suffice for an explanation. (There's some chatter about the stomach of a fruit fly, but let's not go there.) And while none of the team will definitively state that their find is the 'holy gr-ale,' they note that the newly identified year is 99.5 percent identical to the wild strain portion of lager yeast and yet distinct from every other wild yeast with a known genome.
Last month biogeographer Rob Dunn took us down the "path of yeast resistance" by explaining how brewer's yeast may have been the first species cultivated by humans.
Dunn explained both yeast's co-evolution with civilization and why we might care:
"If yeast has evolved with agriculture and our spread, its genes might also be able to tell part of our story as a kind of 'bioglyph' rewritten with each act of yeast sex, division or mutational change.
"The answer, or at least a big clue, was revealed when scientists decided to construct an evolutionary tree for yeast based on the genes of yeasts found in different foods. When they did, they were in for a surprise. The yeasts in beer, wine, sake and other fermented drinks and foods were different, very different, from each other. Those differences were ancient. Yeast does not just colonize any old food out of the hovering ether. It evolved and diversified as civilization and agriculture have evolved and diversified. Out of a few or even just one ancestral yeast strain, many new varieties have emerged. Just as from wolves came big dogs, small dogs, furry dogs and bald dogs, from one or a few yeast strains came all of the alcoholic flavors that we hold so dear."