#FEMSmicroBlog: Searching for the missing parent of the lager yeast in Europe


Beer brewing has been around for many hundreds of years with lager beers becoming popular in Europe around 500 years ago. Lager beer fermentation requires the lager yeast strain Saccharomyces pastorianus, a hybrid of the well-characterized Saccharomyces cerevisiae and the lesser-known Saccharomyces eubayanus. Saccharomyces eubayanus was first isolated in South America in 2011 and since then was also found in Asia, North America and New Zealand – but never in Europe. This created a conundrum: Saccharomyces pastorianus arose in Europe but there was no evidence that one of its parents had ever been to Europe! Now, the study “Identification of European isolates of the lager yeast parent Saccharomyces eubayanus” in FEMS Yeast Research isolated two parental strains in Dublin, Ireland, and reduced the geographical gap. #FascinatingMicrobes

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***This blog entry and the associated press release has been translated into several languages***

Saccharomyces cerevisiae and Saccharomyces eubayanus – parents of the designated lager yeast

When monks in the middle age in German Bavaria started brewing lager beers, they probably did not think that 500 years later we would still marvel at their fermentation product. Not only are lager beers the most-sold beers worldwide, but also, Bavarian lager fermentation led to the birth of a new yeast hybrid.

For thousands of years and still today, Saccharomyces cerevisiae has been used for the production of ale-style beer. However, in the 15th and 16th centuries, laws such as the Bavarian Reinheitsgebot of 1516 restricted beer brewing to the colder winter months and encouraged bottom fermentation.

Scientists agree that in one such brewery, Saccharomyces cerevisiae paired with another yeast species and created the hybrid Saccharomyces pastorianus. This cold-tolerant yeast off-spring became the designated fermenter of lager beers. For many years, scientists were looking for its second parent.

In 2011, Saccharomyces eubayanus was isolated in the Patagonian Andes in South America and seemed to be the second parent of Saccharomyces pastorianus. In the following years, more isolates were found in China, Tibet, New Zealand and North America.

Yet, Saccharomyces pastorianus most likely originated in a Bavarian brewery. So, the question arose: Why had no one found Saccharomyces eubayanus in Europe so far?

The lager yeast Saccharomyces pastorianus arose as a hybrid in Germany in the 15th century, so both parental populations must have been in Europe at that time. John Morrissey, Editor-in-Chief of FEMS Yeast Research

The study Identification of European isolates of the lager yeast parent Saccharomyces eubayanusin FEMS Yeast Research now isolated two Saccharomyces eubayanus strains in Dublin, Ireland. Interestingly, the discovery arose as part of an undergraduate research programme. On an annual “yeast hunting” expedition, students at University College Dublin found the strains of Saccharomyces eubayanus in a wooded area on the University campus.


Irish Saccharomyces eubayanus is not the closest relative to the lager yeast parent

As expected for Saccharomyces eubayanus, the isolates grow at cooler temperatures. But the new strains also sparked new mysteries. For example, Saccharomyces pastorianus is able to transport and consume glucose, maltose and maltotriose with designated transporters for each sugar. Since Saccharomyces cerevisiae does not contain any functional genes for a maltotriose transporter, it was assumed that the gene for the maltotriose transporter must come from Saccharomyces eubayanus. However, the Irish Saccharomyces eubayanus isolate does not contain any gene for a maltotriose transporter.

Additionally, the study shows that the Irish isolate grows poorly on maltose. These two findings indicate that it is unlikely that the Irish isolate is the direct parent of modern lager yeast.

The study also analyses the evolutionary relationships of the Saccharomyces eubayanus isolates. Based on previous studies, Saccharomyces eubayanus can be divided into distinct clades, with the largest diversity found in South America.

Phylogeny of Irist Saccharomyces eubayanus isolates.
Phylogeny of Irish Saccharomyces eubayanus isolates. From Bergin et al. (2022).

The new Irish isolates belong to the Holarctic clade, which also contains isolates from Asia and North America – but not from Patagonia. The part of the Saccharomyces pastorianus genome that comes from Saccharomyces eubayanus also clusters with the Holarctic clade.

Interestingly, although they come from the same clade, isolates from Tibet are more similar to Saccharomyces pastorianus than are the newly identified Irish isolates. This suggests that neither of the Irish isolates is a direct parent of the modern lager yeast.

Thus, the new study proves the existence of a European Saccharomyces eubayanus population. At the same time, it also leads to the question of whether the Saccharomyces eubayanus parent strain still exists in Europe or whether it went extinct and now only lives through its progeny, Saccharomyces pastorianus.

Despite of all the impressive advances at the molecular, cellular and evolutionary level, our understanding of yeast ecology is still rudimentary. José Paulo Sampaio, author of Saccharomyces eubayanus – a tale of endless mysteries

Further possibilities are that more than one hybridization event occurred or several adaptive mutations occurred in the original Saccharomyces pastorianus strain. While mysteries around Saccharomyces eubayanus still need to be unravelled, this study brought us one step closer to the origins of lager beer fermentation.


About the author of this blog

headshot of Dr Sarah Wettstadt: science writer and science communicatorDr Sarah Wettstadt is a microbiologist-turned science writer and communicator writing for professional associations and life science organisations. She publishes the blog BacterialWorld to share the beauty of microbes and bacteria, is a content writer for QIAGEN and blog commissioner for the #FEMSmicroBlog. Her overall vision is to empower through learning, which is why she founded SciComm Society to coach scientists in science communication. To spark interest in science at a younger age, Sarah coordinates workshops in schools for Native Scientist in Alicante. Previous to her science communication career, she did a PhD at Imperial College London, UK, and a postdoc at the CSIC in Granada, Spain. In her non-science time, Sarah enjoys the sunny beaches in Spain playing beach volleyball or travels the world.

About this blog section

The section #FascinatingMicrobes for the #FEMSmicroBlog explains the science behind a paper and highlights the significance and broader context of a recent finding. One of the main goals is to share the fascinating spectrum of microbes across all fields of microbiology.

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