Before beer became lager, a microbe took a mysterious journey

As the story goes, long ago in Bavaria beer underwent a transformation. Dark beer evolved into a paler, golden drink, and the drink became much more common during the era when a ducal edict limited brewing to the winter months. Lager, as the new beer was called, had begun its journey to world domination.

Centuries later, geneticists discovered that the yeast responsible for fermenting lager beers is a hybrid of traditional brewer’s yeast and another cold-hardy yeast, Saccharomyces eubayanus.. The lager yeast appears to be the result of a chance mating in a cold brewery, where low temperatures allowed the hybrid to thrive.

But while brewer’s yeast is fairly common, how lager yeast’s other parent ended up in Bavaria has been harder to trace. It was first spotted in the wild in 2011, when biologists discovered the cold-loving yeast, S. eubayanus, happily living in the forests of Patagonia in South America. Then there were tantalizing traces found in the Italian Alps, Tibet, western China and North Carolina.

So far sightings in Europe have been almost non-existent. But in an article published Wednesday in the journal FEMS Yeast, biologists reported that they found S. eubayanus alive and healthy, living in dirt on the campus of University College Dublin in Ireland. The discovery may provide a key clue to the microbe’s travels: if more samples are found across Europe, we may have a better idea of ​​what led to this chance encounter in a cold Bavarian cellar.

The Irish soil samples were collected by Stephen Allen, an undergraduate student on a laboratory course at University College Dublin led by genetics professor Geraldine Butler and colleagues. When the team got a glimpse of what was living in the dirt, Dr. Butler had a hunch that one of the yeasts was the much sought after S. eubayanus.. Firm identification had to wait until the microbe’s entire genome was sequenced, a process that took several weeks.

“I was kind of sitting on top of the sequencer, waiting for the data to come out,” Dr. Butler said.

Indeed, Mr. Allen’s samples yielded a pair of S. eubayanus strains, and they appeared to belong to the same branch of the family as the versions found in Tibet and North Carolina.

The finding matches climate modeling suggesting Ireland would be a hospitable environment for yeast, said Chris Hittinger, a professor of genetics at the University of Wisconsin – Madison, who was part of the team that found the yeast in Patagonia and is not involved in the current. study. What is less clear is why yeast has been so difficult to find in nature beyond South America, where it grows abundantly in association with beech trees and is considered a native species.

S. eubayanus appears to be less abundant elsewhere, Dr. Hittinger said, so researchers must carefully grow yeast in the lab to have enough to sequence their genomes.

“I think the discovery in Europe now suggests that investing in this effort will be worth it,” he said.

Digging up S. eubayanus in more places could help researchers begin to see how its genetic diversity varies across the planet, which could shed light on how a yeast from South America circled the globe to help revive lager brewing in Bavaria.

“There is a route issue,” Dr. Butler said. “Tibetan yeast is a slightly closer relative of lager yeast than Irish ones,” suggesting that the yeast may have arrived in Germany via Asia – although it’s impossible to say without more samples.

The yeast could have been traveling the earth long before humans entered the scene, perhaps by hitchhiking on birds and insects, Dr. Hittinger said.

For its part, Dr. Butler’s group will continue its research on its university campus in search of S. eubayanus. Members are also curious about some more practical features of the organization.

“We’re interested to see what kind of beer it will make,” she said.