Evidence for Two Main Domestication Trajectories in Saccharomyces cerevisiae Linked to Distinct Bread-Making Processes.

Production of leavened bread dates to the second millennium BCE. Since then, the art of bread making has developed, yet the evolution of bread-associated microbial species remains largely unknown. Nowadays, leavened bread is made either by using a pure commercial culture of the yeast Saccharomyces cerevisiae or by propagating a sourdough-a mix of flour and water spontaneously fermented by yeasts and bacteria. We studied the domestication of S. cerevisiae originating from industrial sources and artisanal sourdoughs and tested whether different bread-making processes led to population divergence. We found that S. cerevisiae bakery strains are polyphyletic with 67% of strains clustering into two main clades: most industrial strains were tetraploid and clustered with strains having diverse origins, including beer. By contrast, most sourdough strains were diploid and grouped in a second clade of strains having mosaic genomes and diverse origins, including fruits and natural environments. They harbored a higher copy number of genes involved in maltose utilization, and a high level of gene flow from multiple contributors was detected. Bakery strains displayed higher CO2 production than do strains from other domesticated lineages (such as beer and wine), revealing a specific phenotypic signature of domestication. Interestingly, industrial strains had a shorter fermentation onset than sourdough strains, which were better adapted to a sourdough-like environment, suggesting divergent selection by industrial and artisanal processes. Our results reveal that the domestication of bakery yeast has been accompanied by dispersion, hybridization, and divergent selection through industrial and artisanal processes.