A wasp feeding on a grape in a Tuscan vineyard. Certain wasps can break and eat grape berries, moving <i>S. cerevisiae</i> yeasts and other microorganisms.

A wasp feeding on a grape in a Tuscan vineyard. Certain wasps can break and eat grape berries, moving S. cerevisiae yeasts and other microorganisms.

Stefano Turillazzi

Brewer’s yeasts mate inside the guts of hibernating wasps

If you can tell French Chardonnay from Italian, you might have an annoying insect to thank. Microbes that live on grape plants—specifically, yeast of the species Saccharomyces cerevisiae—vary from place to place in ways that cause subtle but detectable differences in the taste of the resulting wine. Now, researchers have found that different strains of the yeast mingle and mate like crazy inside the guts of hibernating wasps. The findings suggest that wasps might help to foster yeast biodiversity, with important implications for ecology and industry.

S. cerevisiae is one of the most widely cultivated fungi in the world—used not only in winemaking, but also in baking, brewing, and lab experiments. But researchers have known little about its ecology in the wild, where it grows on ripe fruit.

Thanks to the new results, reported online today in the Proceedings of the National Academy of Sciences, they know a lot more. “It’s the first evidence that shows that in the gut environment, S. cerevisiae can [produce spores], germinate, and mate,” says Duccio Cavalieri, a biologist at the University of Florence in Italy, who led the project.

When Cavalieri and his collaborators first reported finding yeast in wasp intestines in a 2012 paper, they speculated that wasps feeding on yeasty grapes might transfer the yeast from fruit to fruit during warmer months and provide a safe place for it to wait out the winter. But they didn’t know what happened to the yeast during its months inside a hibernating wasp.

To find out, they fed European paper wasps five different strains of S. cerevisiae each. After letting the wasps hibernate for as long as 4 months, they compared the gut-dwelling yeast with colonies that came from the same starting strains but were grown in the lab instead. The different S. cerevisiae strains from the wasps had bred with each other just as much as they had in the controls. In addition, some of the wasps’ S. cerevisiae strains had mated with S. paradoxus, a related species of wild yeast that doesn’t normally breed with S. cerevisiae in the wild.

Together, the results show that the wasp’s belly is more than just a holding chamber for yeast. The yeast are “living, dying, battling for resources, all within this wasp,” says Anne Madden, a microbiologist at the University of Colorado, Boulder, and North Carolina State University in Raleigh, who was not involved in the study.

The fact that S. cerevisiae and S. paradoxus were able to mate inside the wasps means the gut environment could propagate hybrid strains that wouldn’t otherwise occur, the researchers argue.

The findings suggest that wasps may be much more important than usually thought, Madden says. “What’s often perceived as a pest species by humans can have incredible relevance, not only to our understanding of greater ecology, but in terms of having real commercial and industrial value,” she says. “What we’re beginning to learn is that there’s wide unexplored world of microbes and bugs—insects, spiders, mites.”

For instance, beers and wines have regional flavor difference influenced in part by their microbes, including yeasts. “Maintaining this uniqueness requires maintaining the uniqueness of the microbial communities,” says Cavalieri, who comes from a long line of vintners. Wasps could help. But he also thinks there’s a larger ecological context for the work.

“We normally wage chemical warfare against insects all over the place,” he says. “What our findings are basically saying is that if we continue killing the wasps, we lose a fundamental part of the ecological cycle.” Cavalieri’s team is investigating whether similar processes occur in other insects, such as ants.

Not everyone is convinced. Matthew Goddard, a biologist at the University of Lincoln in the United Kingdom, and the University of Auckland in New Zealand, notes that the team didn’t directly demonstrate that the yeast reproduced within the gut. But Cavalieri says his group’s microbiology techniques make it extremely unlikely that the yeast formed cross-species hybrids after they were removed from the wasps.

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