Beer yeast adapted to life with humans

Long before scientists discovered the existence of microorganisms, humans domesticated yeast, coaxing the organism to make palatable beer in exchange for a reliable supply of food and a stable existence. A comprehensive genetic and phenotypic analysis of 157 Saccharomyces cerevisiae yeast strains used in fermentation industries reveals that beer-making yeasts originate from a few common ancestors that quickly evolved ways to satisfy their brewmasters (Cell 2016, DOI: 10.1016/j.cell.2016.08.020). A team led by Kevin J. Verstrepen and Steven Maere of the Flemish Institute for Biotechnology found that, compared with wild yeast, beer yeast has duplicated genes that help the organism break down maltotriose, a sugar found in beer mash. Many beer yeast strains have also evolved mutations that prevent production of 4-vinylguaiacol, an off-flavor in many beers. Meanwhile, because beer yeast is used continuously from one batch to another, it has lost the ability to reproduce sexually, the researchers found, a skill the organisms would need to survive and to adapt to stressful environments in the wild. By comparison, the team found that wine yeast still retains the ability to reproduce sexually, probably because wine making occurs only in autumn, leaving the yeast to fend for themselves during the rest of the year.