''Saccharomyces eubayanus'', a cryotolerant (cold tolerant) type of

yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom (biology), kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are est ...

, is most likely the parent of the

lager Lager (; ) is a Type of beer, style of beer brewed and Brewing#Conditioning, conditioned at low temperature. Lagers can be Pale lager, pale, Amber lager, amber, or Dark lager, dark. Pale lager is the most widely consumed and commercially availab ...

brewing yeast, ''

Saccharomyces pastorianus ''Saccharomyces pastorianus'' is a yeast used industrially for the production of lager beer, and was named in honour of Louis Pasteur by the German Max Reess in 1870. This yeast's complicated genome appears to be the result of Hybridisation (bio ...

''.. Lager is a type of

beer Beer is an alcoholic beverage produced by the brewing and fermentation of starches from cereal grain—most commonly malted barley, although wheat, maize (corn), rice, and oats are also used. The grain is mashed to convert starch in the ...

created from malted

barley Barley (), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains; it was domesticated in the Fertile Crescent around 9000 BC, giving it nonshattering spikele ...

and fermented at low temperatures, originally in Bavaria. ''S. eubayanus'' was first discovered in

Patagonia Patagonia () is a geographical region that includes parts of Argentina and Chile at the southern end of South America. The region includes the southern section of the Andes mountain chain with lakes, fjords, temperate rainforests, and glaciers ...

, possibly being an example of

Columbian exchange The Columbian exchange, also known as the Columbian interchange, was the widespread transfer of plants, animals, and diseases between the New World (the Americas) in the Western Hemisphere, and the Old World (Afro-Eurasia) in the Eastern Hemis ...

, and is capable of fermenting

glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...

, along with the disaccharide

maltose } Maltose ( or ), also known as maltobiose or malt sugar, is a disaccharide formed from two units of glucose joined with an α(1→4) bond. In the isomer isomaltose, the two glucose molecules are joined with an α(1→6) bond. Maltose is the tw ...

at reduced temperatures.

History

With the emergence of lager beer in the 14th century, S. ''eubayanus'' was considered to be the progenitor of S. ''pastorianus'' along with S. ''cerevisiae''. Since 1985 the non-''cerevisiae'' ancestor has been contentiously debated between S. ''eubayanus'', and S. ''bayanus'' which "is not found outside the brewing environment". Upon the 2011 discovery of S. ''eubayanus'' in Argentina and consequential genome analysis, S. ''eubayanus'' was found to be 99% genetically identical to S. ''pastorianus'' and S. ''bayanus'' was dismissed as an ancestor. First described in 2011, S. ''eubayanus'' was discovered in North

, ecologically associated with ''

Nothofagus ''Nothofagus'', also known as the southern beeches, is a genus of 43 species of trees and shrubs native to the Southern Hemisphere, found across southern South America (Chile, Argentina) and east and southeast Australia, New Zealand, New Guin ...

'' spp. (Southern Beech) forests and the parasitic biotrophic fungi '' Cyttaria'' spp. With discoveries in other parts of the world shortly after in east Asia, the South American origins of S. ''eubayanus'' have been challenged by

genomic Genomics is an interdisciplinary field of molecular biology focusing on the structure, function, evolution, mapping, and editing of genomes. A genome is an organism's complete set of DNA, including all of its genes as well as its hierarchical, ...

and

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

evidence that suggests a Tibetan origin. The proponents of this theory argue that it "corresponds better with geography and world trade history" given the Eurasian land bridge. Since then, genomic analyses from South America strains have shown reduced genetic diversity suggesting a biogeographical radiation point from Patagonia. In 2022, a researcher team from the University College Dublin isolated ''Saccharomyces eubayanus'' from soil samples in Ireland. Further isolations from different locations in Europe can be expected. Phylogenetically, S. ''eubayanus'' is basal in the Saccharomyces genus, and well-adjusted to the cooler environment of ''Nothofagus'' forests, Saccharomyces species with thermo-tolerance are suggested to be derived traits.

Genomics

Population genomic analyses have identified two main populations of S. ''eubayanus'' located in Patagonia, Patagonia A and Patagonia B/Holarctic. "These are the closest known wild relatives of the Lager yeasts", comparing sub-genomes, the wild strains are 99.82% and 99.72% identical respectively. Lager yeasts consist of two distinct lineages, said to have been hybridized from independent events 1000 years ago. Type one, called Saaz contains the allotriploid strains with one copy of the S. ''cerevisiae'' genome and two copies of the S. ''eubayanus'' genome. The second type, Frohberg, houses allotetraploid strains with one full diploid genome copy of S. ''cerevisiae'' and S. ''eubayanus''. Saaz strains, which are more physiologically similar to their S. ''eubayanus'' parent, are much more efficient at growing in low temperatures, reflecting S. ''eubayanus''' cryotolerant properties. S. ''eubayanus'' is said to provide the bottom-fermentation and cold temperature genetics that distinguish this ssp. from the top-brewing and bread making relative S. ''cerevisiae''. A de novo assembly of the S. ''eubayanus'' genome yielded 5,515 protein-coding genes, 4,993 of which were unambiguous 1:1 orthologs to S. ''cerevisiae'', and S. ''uvarum''.

Uses

In 2015, an interspecific hybridization of S. ''cerevisiae'' and S. ''eubayanus'' was successful in creating novel lager brewing yeasts. However hybrid genomes can result in genetic instability in industrial uses. In 2016, ''S. eubayanus'' was used itself to brew lager beer.HEINEKEN introduces H41 ‘Wild Lager’, by Heineken
6 Apr 2017. WebArchive as of 26 Oct 2020

References

{{Taxonbar, from=Q2784012 eubayanus Yeasts used in brewing Fungi described in 2011 Fungus species