Summer temperature can predict the distribution of wild yeast populations

The wine yeast, Saccharomyces cerevisiae, is the best understood microbial eukaryote at the molecular and cellular level, yet its natural geographic distribution is unknown. Here we report the results of a field survey for S.cerevisiae, S.paradoxus and other budding yeast on oak trees in Europe. We show that yeast species differ in their geographic distributions, and investigated which ecological variables can predict the isolation rate of S.paradoxus, the most abundant species. We find a positive association between trunk girth and S.paradoxus abundance suggesting that older trees harbor more yeast. S.paradoxus isolation frequency is also associated with summer temperature, showing highest isolation rates at intermediate temperatures. Using our statistical model, we estimated a range of summer temperatures at which we expect high S.paradoxus isolation rates, and show that the geographic distribution predicted by this optimum temperature range is consistent with the worldwide distribution of sites where S.paradoxus has been isolated. Using laboratory estimates of optimal growth temperatures for S.cerevisiae relative to S.paradoxus, we also estimated an optimum range of summer temperatures for S.cerevisiae. The geographic distribution of these optimum temperatures is consistent with the locations where wild S.cerevisiae have been reported, and can explain why only human-associated S.cerevisiae strains are isolated at northernmost latitudes. Our results provide a starting point for targeted isolation of S.cerevisiae from natural habitats, which could lead to a better understanding of climate associations and natural history in this important model microbe.