According to a new study in the academic journal journal Cell Reports, microbiologists have figured out why Brewer’s yeast, also known as S. cerevisiae, produces its characteristic earthy smell. It turns out the rich, ripening fruit scent attracts fruit flies, which then collect yeast on their legs and heads and disperse the yeast cells in the environment.

Of note, yeast lacking a single aroma-producing gene fail to create the characteristic odor, nor do they attract fruit flies.

Brewer's Yeast And Fruit Flies Have Unusual Symbiotic Relationship

Statement from lead researcher

“Two seemingly unrelated species, yeasts and flies, have developed an intricate symbiosis based on smell,” said Kevin Verstrepen of KU Leuven and VIB in Belgium in explaining the study. “The flies can feed on the yeasts, and the yeasts benefit from the movement of the flies.”

Details on the Brewer’s yeast and fruit fly study

Verstrepen got the idea for the project 15 years ago as a grad student doing research into how yeast cells contribute to the flavor of beer and wine. He determined that yeast cells produce a number of aroma compounds similar to those produced by ripening fruits. One yeast gene in particular, called ATF1, led to the production of most of those volatile chemicals.

He recounted a memorable incident back in his grad school days: “When returning to the lab after a weekend, I found that a flask with a smelly yeast culture was infested by fruit flies that had escaped from a neighboring genetics lab, whereas another flask that contained a mutant yeast strain in which the aroma gene was deleted did not contain any flies.”

But it was many years later — when he began to work with fruit fly neurobiologists Emre Yaksi and Bassem Hassan — that the project came together at last.

Using molecular biology and neurobiological methods as well as behavioral tests, the Verstrepen and colleagues managed to demonstrate that loss of the ATF1 gene changes the reaction in the fruit fly brain to the smell of yeast. This means flies are much less attracted to the mutant ATF1-free yeast cells, which by the same token led to reduced dispersal of mutant yeast by the flies.

The results highlight an unknown until now aroma-based communication and symbiosis between microbes and insects. The scientists say they suspect that similar mechanisms likely exist in other plant-associated microbes, including pathogens.

The research team has managed to isolate a number of different yeast species from the bodies of fruit flies and discovered that almost all those yeasts create aroma compounds. The researchers also isolated several powerful aroma-producing yeasts from flowers.

“These preliminary results suggest that aroma production is not restricted to S. cerevisiae and may be a much more general theme in microbe-insect interactions,” they noted in their article in Cell Reports.