Reconstruction of the genome origins and evolution of the hybrid lager yeast Saccharomyces pastorianus

Abstract

Inter-specific hybridization leading to abrupt speciation is a well-known, common mechanism in angiosperm evolution; only recently, however, have similar hybridization and speciation mechanisms been documented to occur frequently among the closely related group of sensu stricto Saccharomyces yeasts. The economically important lager beer yeast Saccharomyces pastorianus is such a hybrid, formed by the union of Saccharomyces cerevisiae and Saccharomyces bayanus-related yeasts; efforts to understand its complex genome, searching for both biological and brewing-related insights, have been underway since its hybrid nature was first discovered. It had been generally thought that a single hybridization event resulted in a unique S. pastorianus species, but it has been recently postulated that there have been two or more hybridization events. Here, we show that there may have been two independent origins of S. pastorianus strains, and that each independent group—defined by characteristic genome rearrangements, copy number variations, ploidy differences, and DNA sequence polymorphisms—is correlated with specific breweries and/or geographic locations. Finally, by reconstructing common ancestral genomes via array-CGH data analysis and by comparing representative DNA sequences of the S. pastorianus strains with those of many different S. cerevisiae isolates, we have determined that the most likely S. cerevisiae ancestral parent for each of the independent S. pastorianus groups was an ale yeast, with different, but closely related ale strains contributing to each group’s parentage.

125th Anniversary Review: Yeast Flocculation and Sedimentation in Brewing

“…Lager strains are allopolyploid hybrids of Saccharomyces cerevisiae and a Saccharomyces bayanus-like yeast 15,53 that was recently identified as Saccharomyces eubayanus sp. nov. 44 .…”

Isolation of Meiotic Segregants from a Bottom Fermenting Yeast

“…At any rate, it is obvious that array-CGH showed that the genotypes of meiotic segregants possessing both Lg-FLO1 and ILF1 had an increased copy number of the right end of SC-type chromosome VIII. Previous studies 1,2,12 reported that aneuploidy was also observed among bottom fermenting yeast strains. Most meiotic segregants have wort fermentability and are therefore valuable for the brewing industry.…”

Yeast: World’s Finest Chef

“…Usually these complex genomes are tetraploid, which may result from the fusion of diploid parental strains or from duplication of the genetic information after the original cell fusion. Analysis on lager yeast genomes revealed other changes such as chromosome loss and/or duplications, likely due to human selection of relevant phenotypes [33,34]. In reference [34] lager yeast genomes were analysed and classified in two groups.…”

“…Analysis on lager yeast genomes revealed other changes such as chromosome loss and/or duplications, likely due to human selection of relevant phenotypes [33,34]. In reference [34] lager yeast genomes were analysed and classified in two groups. In group I, cells present one S. cerevisiae genome equivalent and, in group II, cells present two S. cerevisiae genome equivalents.…”

“…As for ale yeasts, studies revealed that these strains are closely to S. cerevisiae [34,36]. In fact, a genotype analysis of 651 S. cerevisiae strains revealed that ale strains were more closely related to wine and bread strains (above referred as Baker's yeast), than to lager brewer's yeast strains [36].…”