Abstract
Strains of Saccharomyces cerevisiae used to make beer, bread, and wine are genetically and phenotypically distinct from wild populations associated with trees. The origins of these domesticated populations are not always clear; human-associated migration and admixture with wild populations have had a strong impact on S. cerevisiae population structure. We examined the population genetic history of beer strains and found that ale strains and the S. cerevisiae portion of allotetraploid lager strains were derived from admixture between populations closely related to European grape wine strains and Asian rice wine strains. Similar to both lager and baking strains, ale strains are polyploid, providing them with a passive means of remaining isolated from other populations and providing us with a living relic of their ancestral hybridization. To reconstruct their polyploid origin, we phased the genomes of two ale strains and found ale haplotypes to both be recombinants between European and Asian alleles and to also contain novel alleles derived from extinct or as yet uncharacterized populations. We conclude that modern beer strains are the product of a historical melting pot of fermentation technology.
Highlights
The brewer’s yeast Saccharomyces cerevisiae is known for its strong fermentative characteristics
To determine the ancestry of beer strains, we compared the genomes of beer strains with the genomes of a large collection of strains isolated from diverse sources and geographic locations
We found ale, baking, and the S. cerevisiae portion of lager strains to have ancestry that is a mixture of European grape wine strains and Asian rice wine strains and that they carry novel alleles from an extinct or uncharacterized population
Summary
The brewer’s yeast Saccharomyces cerevisiae is known for its strong fermentative characteristics. The preference for fermentation in the presence of oxygen arose as a multistep evolutionary process around the time of an ancient genome duplication, endowing numerous species with the ability to produce levels of ethanol toxic to many microorganisms [1,2] One of these species, S. cerevisiae, gained the ability to competitively dominate many other species in high-sugar, low-nutrient environments, such as grape must [3]. Besides S. cerevisiae, the most widely used species is S. pastorianus, an allopolyploid hybrid of S. cerevisiae and S. eubayanus, used to make lager beer [7] The use of this hybrid emerged during the 15th century in Europe and was formed from an S. eubayanus strain closely related to wild populations from North America and Tibet [9,10] and a S. cerevisiae strain related to those used to ferment ales [11,12,13]. The origin of ale and other domesticated strains of S. cerevisiae is beginning to emerge through comparison with wild populations [12,13,14,15,16]
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