Sourdough yeasts from a genomic perspective

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Current Biology has a fascinating paper by Frédéric Bigey and coworkers examining the genomic variation of bakery yeasts: “Evidence for Two Main Domestication Trajectories in Saccharomyces cerevisiae Linked to Distinct Bread-Making Processes”. In this year of sourdough backing, it is neat to see the differentiation of yeasts maintained in artisanal sourdough cultures in comparison to industrial baking.

I’ve been keeping a sourdough this year and enjoy trying different recipes with it. There’s a widespread idea in the culture of bakers that sourdough yeasts are basically wild, easily captured from fruit or other natural sources. It’s of course true that you can start a sourdough from lots of different yeasts. But what’s interesting in this paper is that yeasts that are in long-maintained sourdoughs are really quite specific. They are diverse compared to commercial baking yeasts, but they fall along a specific branch of the tree of Saccharomyces cerevisiae, with wine and beer yeasts covering a yet broader diversity of branches.

The authors’ conclusions about sourdough are that the human-made environment has mattered a lot.

Sourdough is a human-made habitat. One may consider that any yeast population originating from sourdough is domesticated because this environment would not exist without human intervention. Alternatively, one may consider that sourdough yeast populations can only be considered domesticated if some selection imposed by the baking process has indeed occurred. Here, we suggest that sourdough strains are not only present in their environment by chance or by recurrent introduction but could have been selected for better fermentation performance through bakery processes. They compared to commercial strains in terms of CO2 production but reached a higher population size at the end of fermentation in synthetic sourdoughs. They also displayed better growth on maltose than commercial strains. These results suggest that sourdough strains are indeed better adapted to a sourdough environment and provide interesting genetic resources for improving sour- dough-bread-making processes. Sourdough yeasts co-occur with lactic acid bacteria. Future work on yeasts-bacteria interaction will likely shed additional light on their possible coevolution in a sourdough environment.

There is much discussion of “accidental domestication” in the early phases of animal and plant domestication. The idea is that human activities create environments that animals or plants adapted to without direct human breeding. This kind of incidental adaptation to human-altered environments is widespread today. Looking at human-made microenvironments is a promising avenue to look at the mechanisms of domestication.