While you may not catch a fly sipping Perrier, the insect has specialized taste cells for carbonated water that probably encourage it to binge on food with growing microorganisms. Yeast and bacteria both produce carbon dioxide (CO2) when they feast, and CO2 dissolves readily in water to produce seltzer or soda water.
This is one of the first, if not the only taste sensation discovered in animals beyond the five that humans taste - sweet, sour, bitter, salty and umami, or savory.
"This was unexpected, because fruit flies also smell CO2 and they avoid it," said neurobiologist Kristin Scott, assistant professor of molecular and cell biology at UC Berkeley. "One way that we like to think of it is that flies seek the right amount of rottenness - if fruit is only half rotten, producing a little CO2, it's good; if too rotten, it gives off a lot of CO2 and is bad tasting. They seek a balance."
Scott and her UC Berkeley colleagues, graduate students Walter Fischler, technician Priscilla Kong and postdoctoral fellow Sunanda Marella - all in the Department of Molecular and Cell Biology and the Helen Wills Neuroscience Institute - report their discovery in the Aug. 30 issue of Nature.
Mammals have five known types of taste receptors, though there may be more to discover, Scott said. Flies may have five distinct receptors also, but not the same ones mammals have. While Scott has shown that fruit flies can detect sweet and bitter compounds, and now carbonation, she has discounted their ability to taste umami and said that their ability to taste sour compounds is questionable. She and her lab continue to investigate other unknown taste modalities in fruit flies, which could be any of a number of tastes, such as salt or alcohol.
The discovery came when Fischler, frustrated that he could not find a chemical that stimulated an unknown type of fruit fly taste cell he had isolated, tested the cells' reaction to a drop of Samuel Adams beer. Surprised by a positive response, he tried to narrow down the taste preference to one of the many chemicals in beer. Flat beer and dry yeast, for example, did not work. That's when he discovered the leftover bottle of Calistoga mineral water.
As he was searching for beer components to test, he said, "I opened the refrigerator and looked in, when a light bulb went on. Calistoga would be a great way of testing CO2."
The rest is history. Dry ice - frozen CO2 - produced a strong response, while high levels of gaseous CO2 produced a weak response in the taste cells. Sodium bicarbonate in a basic solution that does not contain CO2 bubbles did not work; bicarbonate in a solution with CO2 bubbles did. The liquid in which yeast grow, though not the yeast themselves, also elicited a response from the taste cell. These and a few other genetic tests narrowed the taste trigger down to dissolved carbon dioxide.
The preference for carbonation is weak compared with that for sweetness, Scott noted, implying that seltzer enhances taste or makes other tastes more acceptable. This makes sense because CO2 has no nutritional value, but is a byproduct of organisms - yeast and bacteria - that do provide nutrients, she said.
The newly discovered taste sensors for carbonation reside on their own structures, called taste pegs, on the tongue of the fly. While a fruit fly's four other taste cells are perched on the tip of bristles that cover the entire body, the carbonated water taste cells are clustered around the margins of the sponge-like tip of the proboscis, at the base of taste bristles.
Scott investigates taste cells, which are a type of nerve cell, and is characterizing the cells and genes associated with different tastes. So far, she and her laboratory colleagues have identified the sweet and bitter cells and some of the gustatory receptor genes that detect sweet and bitter compounds in fruit flies.
Fischler now is trying to isolate the actual receptor in the CO2-sensing nerve cell that grabs the CO2 molecule and sends a signal to the fly brain that there is carbonation in the food. It will then be possible to see if others, including humans, also have carbonation receptors on taste cells.
"There may be many more taste modalities in humans" than the five known today, said Scott. Even if CO2 is a taste unique to fruit flies, it's discovery suggests that other animals may have taste receptors tuned to important chemicals in their environment, she said, either to avoid them, as is the case with bitter chemicals, or seek them out, as is the case with sugars and CO2.
"Thus, taste modalities may differ according to nutritional needs," she and her colleagues wrote. "Alternatively, CO2 may be an unappreciated taste modality in many organisms."
Robert Sanders | EurekAlert!
Multi-institutional collaboration uncovers how molecular machines assemble
02.12.2016 | Salk Institute
Fertilized egg cells trigger and monitor loss of sperm’s epigenetic memory
02.12.2016 | IMBA - Institut für Molekulare Biotechnologie der Österreichischen Akademie der Wissenschaften GmbH
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water
In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...
The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.
Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
02.12.2016 | Medical Engineering
02.12.2016 | Agricultural and Forestry Science
02.12.2016 | Physics and Astronomy