(U-WIRE) BERKELEY, Calif. — Fruit flies’ affinity for beer tipped off a group of University of California at Berkeley researchers to a taste receptor sensitive to carbonation.

A study published last week in the scientific journal Nature is part of the team’s ongoing investigation of the taste circuits of fruit flies being conducted in an attempt to understand how brains process sensory information, said Kristin Scott, the assistant professor of molecular cell biology heading the project.

Scott and her colleagues had already determined that fruit flies can detect sweet and bitter tastes, but this study uncovered the first carbon dioxide taste receptors to be found in an organism when the flies’ taste cells responded to beer.

“It’s a new taste modality,” she said. “So other organisms might have other (taste modalities) as well.”

Taste mechanisms in fruit flies work in much the same way as they do in humans, so a carbon dioxide taste receptor in humans is a possibility, she said.

Scott and her team began the project two years ago by isolating fruit fly taste cells that did not respond to classical taste stimuli such as sweetness, bitterness and saltiness, she said.

The researchers tested substances by mapping the fruit flies’ taste cells in the brain and monitoring their responses when stimulated, said Walter Fischler, a graduate student in molecular cell biology who worked on the study.

Finding a chemical that activated these uncategorized taste cells was the most difficult part of the project, Fischler said.

“We knew they were taste cells,” he said. “But until we found a chemical they would respond to, we really didn’t know if we had something interesting or not.”

Fischler said he remembered hearing that flies seem to like beer, so he tested the taste cells with beer and they finally responded.

“It was definitely a ‘eureka’ moment,” he said.

There seemed to be a link between the response to beer and the fact that fruit flies eat yeast, but the cells did not respond to yeast alone, Fischler said.

“That’s when I opened the fridge, just trying to find something, and there was a bottle of Calistoga (carbonated water). It hit me that I could test CO2, since Calistoga is only water and CO2,” he said.

The cells did not react to flat water, but did respond to the Calistoga water, solid carbon dioxide, gaseous carbon dioxide and a bicarbonate solution with carbon dioxide bubbles, Scott said.

This led to the conclusion that it was carbon dioxide- — he carbonation in the beer they had tested — to which the cells were sensitive, Fischler said.

The results make sense because fruit flies lay their eggs on fruit in the process of being decomposed by microorganisms such as yeast, Fischler said. When yeast ferments the fruit’s sugar, it produces CO2 as a byproduct.

Scott said the taste receptors for CO2 may be a way for fruit flies to detect the presence of these microorganisms.

“Our idea is that (CO2 receptors) probably work in conjunction with taste receptors for other substances that are nutritional,” she said. “It may work as a flavor enhancement for the flies, but it probably doesn’t taste very good alone.”

The research team will next work to identify the molecule itself that is detecting CO2, since other tastes are known to be detected by proteins secreted from a taste receptor gene, Fischler said.