Hsp12p and PAU genes are involved in ecological interactions between natural yeast strains

The co-existence of different yeasts in a single vineyard raises the question on how they communicate and why slow growers are not competed out. Genetically modified laboratory strains of Saccharomyces cerevisiae are extensively used to investigate ecological interactions, but little is known about the genes regulating cooperation and competition in ecologically relevant settings. To understand the genetics of ecological interactions, we isolated eight yeast strains from a single vineyard and examined the fitness in single-clone strain cultures of these natural isolates in synthetic wine must simulating their natural environment. We found great differences in the fitness of the eight strains, thus we performed genome-wide analyses in order to identify the genes involved in the establishment of their co-existence in the vineyard. The results highlight the existence of an unexpected altruistic behavior, which mainly depends on a released heat-shock protein, Hsp12p. The altruistic strain also punishes close relatives non-producers by contact dependent transmission of a killer toxin, while a membrane protein (Pau5p) can provide resistance against this toxin. The reward-punishment loop created by the combined action of Hsp12p, Pau5p and killer toxin is sufficient to steer a yeast community and ensure the survival of a cooperating strain.