Scientists have solved the mystery behind the origins of yeasts used to make today's lager.
Lager yeasts are hybrids made from a combination of the S. cerevisiae and S. eubayanus yeast strains. Lagers make up an impressive 94 percent of the modern beer market, but the origins of these hybrid lineages have remained largely unknown, Molecular Biology and Evolution from Oxford University Press reported.
A team of researchers used genome sequencing to look at a newly described wild yeast species from Patagonia called Saccharomyces eubayanus. The genome was compared to those of domesticated hybrids that are used to brew lager style beers, which allowed the scientists to determine the lineages of the two common strains for the first time.
The findings revealed two independent origin events led to the rise of the S. cerevisiae and S. eubanyus hybrids used to brew lager beers. The Saaz and Frohberg lineages (named for their region of origin), were both born from nearly identical strains of S. eubayanus and diverse ale strains of S. cerevisiae.
"Lager yeasts did not just originate once. This unlikely marriage between two species, genetically as different from one another as humans and birds, happened at least twice. Although these hybrids were different from the start, they also changed in some predictable ways during their domestication," said corresponding author Chris Todd Hittinger of the University of Wisconsin-Madison.
Mitochondrial genome sequences, which provide a "blueprint" of the powerhouses of the yeast cell, showed that S. eubayanus was the main donor of mtDNA for lager yeasts of Frohberg lineage. Both Saaz and Frohberg yeasts contained S. cerevisiae and S. eubayanus genomes. The S. eubayanus genomes appeared to have gone through increased rates of evolution, especially in genes linked to metabolism.
"The findings have now clarified the origins of the major lineages of the hybrid yeasts used to brew lagers, and will provide a roadmap for future research in the domestication of lager yeasts," the researchers concluded.
The findings were published in a recent edition of the journal Molecular Biology and Evolution.
