Wasp intestines provide a good mating environment for the yeast that’s responsible for our wine, beer, and bread. The findings, published in Proceedings of the National Academy of Sciences this week, suggest that the gut of wasps are breeding grounds for novel genetic combinations of industrially important yeast that might not meet and mate otherwise. 

The budding yeast Saccharomyces cerevisiae (also known as baker’s or brewer’s yeast) has been a huge part of our fermented products since the beginning of agriculture. Yet we still don’t fully understand their sex lives in the wild. Recent work revealed that insects such as social wasps host S. cerevisiae in their intestines and transport them around. Wine fermentation, for example, begins after wasps leave the yeast behind on grape berries (pictured above). 

To explore the mating behavior of these helpful single-cell microorganisms, a team led by Duccio Cavalieri from the University of Florence conducted genetic analyses on yeast strains, including samples isolated from wineries, grape berries, and the gut of wasps captured out in the wild. Researchers had assumed that brewer’s yeast rarely mate with unrelated yeast strains, but the team found evidence to the contrary within the intestines of Polistes dominula social wasps. In particular, they identified several unlikely yeast hybrids that represent rare crosses between brewer’s yeast and distantly-related strains, including the wild yeast Saccharomyces paradoxus. (These often interact with wasps on tree bark, as seen in the picture below.)

Then, when the team fed different yeast cells to wasps, they discovered that unrelated yeast strains regularly mate. Some of these same interspecific yeast hybrids have been the source of multiple successful industrial yeast strains used to make both beer and wine. Furthermore, two European strains of S. paradoxus can’t even survive in the wasp gut unless it has mated with S. cerevisiae. 

These findings suggest the intestines of social wasps provide S. cerevisiae with an environment that favors mating among themselves as well as outbreeding. Though exactly how the wasp gut favors the process is still under investigation, Cavalieri explains to IFLScience. It’s possible that the long period of inactivity and reduced metabolism that insects undergo during the two months or so of hibernation facilitate the key processes of spore production and germination, as well as hybrid formation. It also takes several hours for insects to wake up and regain activity as the cold slowly decreases. 

“The genetic diversity generated in the wasp’s gut could favor adaptation to the ever-changing fermentative environment,” the authors write. “Preserving the treasure potentially hidden in the gut of vineyard wasps could be relevant from both the ecological and biotechnological standpoints.”

^{A crabro wasp by a nest in a tree. These wasps transport yeast species isolated from tree bark (such as Saccharomyces paradoxus) to different environments. Carlotta De Filippo}