Industrial yeast, generally Saccharomyces cerevisiae, are used to make numerous alcoholic beverages as well as biofuel and bread. They live in human constructed environments and show signs of domestication. Domestication simply means that an organism adapts to a human constructed environment so it can be more successful while losing some of its ability to survive in a wild or natural environment. Yeast domestication started occurring before yeast were even identified as the organism responsible for fermentation. Domestication can normally be identified by changes to polyploidy, phenotypes, and chromosomes as well as the decay and replication of genes.
B. Gallone and associates assessed 181 strains of Saccharomyces cerevisiae yeast in an attempt to understand how much domestication as occurred in industrial yeasts(1). They identified 5 main lineages or clades of yeast that accounted for 124 of these strains. Within these strains, they identified 15,288 instances where the yeast experienced a change in there genes. These changes resulted in variation to the phenotypes of the yeast. Phenotypes are the characteristics that we would use to describe a yeast. The aromas it produces, its ability to process certain types of sugars, and how tolerant it is to alcohol are examples of phenotypes. Yeast identified in the Beer lineage or clade possess the greatest amount of domestication. This is speculated to be from the common practice of top-cropping or back-slopping where active yeast was removed and used to seed a new fermentation.
One interesting finding from B. Gallone and associates was that the deletion of genes were twice as common as a change in the amplification of gene. That means that a yeast is more likely to lose or gain the ability to do something versus having an ability increased or decreased. They also found that the industrial application and geographic location where a yeast is used had an impact on the way the yeast evolved. American beer yeast appear to be closely tied together but also tied to British beer yeast. Their research showcases the knowledge we are gaining as a result of genome sequencing and how it is helping us better understand of how genes work.
Do these words make you want to know more about yeast and fermentation? Harvest and culture yeast to make unique ciders. Checkout The Shop for the plates and tools I use. Here are some other articles on yeast and fermentation. Search PricklyCider.com to find even more.
(1) B. Gallone and associates, Domestication and Divergence of Saccharomyces cerevisiae Beer Yeasts, Cell 166, 1397–1410, 2016
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