Complex origins of lager-brewing hybrids were shaped by standing variation in the wild yeast Saccharomyces eubayanus

PERIS, D.; LANGDON, Q; MORIARTY, RV; SYLVESTER, K; BONTRAGER, M.; CHARRON, G.; LEDUCQ, J-B; LANDRY, CR; LIBKIND, DIEGO; HITTINGER, C

PLOS GENETICS

PUBLIC LIBRARY SCIENCE

Lugar: San Francisco; Año: 2016 vol. 12 p. 1 - 20

1553-7390

Lager-style beers constitute the vast majority of the beer market, and yet, the genetic origin of the yeast strains that brew them has been shrouded in mystery and controversy. Unlike conventional ale-style beers, which are generally brewed with Saccharomyces cerevisiae, lagers are brewed at colder temperatures with allopolyploid hybrids of Saccharomyces eubayanus x S. cerevisiae. Since the discovery of S. eubayanus in 2011, additional strains have been isolated from South America, North America, Oceania, and Asia, but only interspecies hybrids have been isolated in Europe. Here, using genome sequence data, we examine the relationships of these wild S. eubayanus strains to each other and to domesticated lager strains. Our results support the existence of a relatively low-diversity lineage of S. eubayanus whose distribution stretches across the Holarctic region and includes wild isolates from Tibet, new wild isolates from North America, and the S. eubayanus parents of lager yeasts. This clade is closely related to a high-diversity population which is found primarily in South America but includes some widely distributed isolates. This population is closely related to a second high-diversity South American population, while two early-diverging Asian subspecies are more distantly related. We further show that no single Holarctic isolate is the sole closest relative of lager yeasts. Instead, different parts of the genome portray different phylogenetic signals and ancestry, likely due to outcrossing and incomplete lineage sorting. Indeed, standing genetic variation within this wild Holarctic population of S. eubayanus is responsible for genetic variation still segregating among modern lager-brewing hybrids. The surprising observation that the S. eubayanus subgenomes of hybrid strains retain genetic diversity found in the wild suggests that lager yeast origins were complex, underscoring the need for further investigations in the Northern Hemisphere.