beer and flies
October 11, 2014

Intricate Symbiosis: Beer Yeast Creates Aroma To Attract Fruit Flies For Cell Dispersal

Brett Smith for redOrbit.com - Your Universe Online

Beer aficionados prize the frothy beverage of their affection for its taste as well as its smell, but they aren’t the only ones who enjoy the whiff of fermented barley.

According to new research from a team of Belgian scientists published in the journal Cell Reports, the characteristic smell of beer attracts fruit flies, which in turn disperse beer yeast cells.

"Two seemingly unrelated species, yeasts and flies, have developed an intricate symbiosis based on smell," said study author Kevin Verstrepen of KU Leuven and the VIB Laboratory of Systems Biology in Belgium.

Similar yeasts are also used to produce wine – as both sets of yeast consume sugars, from malted barley or grape juice, and convert them into alcohol and carbon dioxide. These microbes also produce aroma as a by-product – aromas that can differentiate a merlot from a pinot noir, or a porter from a lager.

"The importance of yeast in beer brewing has long been underestimated,” Verstrepen said. “But recent research shows that the choice of a particular yeast strain or variety explains differences in taste between different beers and wines.”

“In fact, yeasts may even be responsible for much of the "terroir", the connection between a particular growing area and wine flavor, which previously often was attributed to differences in the soil,” he said.

Verstrepen said the impetus for the new study came from a previous research project involving the yeast gene for alcohol acetyl transferase, known as ATF1, which was behind most of the volatile chemicals created during fermentation.

"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," he said.

In the new study, the team used a mixture of molecular biology, neurobiology and behavioral assessments. They were able to indicate that loss of ATF1 "changes the response of the fruit fly brain to a whiff of yeast. As a result, the flies are much less attracted to the mutant yeast cells, which in turn results in reduced dispersal of mutant yeast by the flies."

The study team concluded that the two kinds of organisms must have a mutualistic relationship and theorized that similar relationships may be present in other plant-associated microbes, including pathogens.

“We all know that flowers attract insects by producing aromas. But there's also a lot of microbes living inside flowers, and the chemicals they produce may also play an important role" said study author Joaquin Christiaens, a PhD student from both VIB and KU Leuven.

Luis Franco, a VIB/KU Leuven PhD student who performed the fly assays, agreed with his colleague.

"There's a lot to be learnt about the mutualism between insects and microbes, and some of what we find may have implications in agriculture and medicine,” he said. “Don't forget that insects also carry disease-causing microbes..."

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