Genomic Stability and Adaptation of Beer Brewing Yeasts During Serial Repitching in the Brewery

Ale brewing yeast are the result of admixture between diverse strains of yeast, resulting in a heterozygous tetraploid that has since undergone numerous genomic rearrangements. As a result, comparisons between the genomes of modern related ale brewing strains show both extensive aneuploidy and mitotic recombination that has resulted in a loss of intragenomic diversity. Similar patterns of intraspecific admixture and subsequent selection for one haplotype have been seen in many domesticated crops, potentially reflecting a general pattern of domestication syndrome between these systems. We set out to explore the evolution of the ale brewing yeast, to understand both polyploid evolution and the process of domestication in the ecologically relevant environment of the brewery. Utilizing a common brewery practice known as repitching, in which yeasts are reused over multiple beer fermentations, we generated a population time-course from multiple breweries utilizing similar strains of ale yeast. Applying whole-genome sequencing to the time-courses, we have found that the same structural variations in the form of aneuploidy and mitotic recombination reproducibly rise to detectable frequency during adaptation to brewing conditions across multiple related strains in different breweries.