Current Weather
The Spy FM

Fruit Fly Nose Says Steer Clear Of Deadly Food; Human Nose Not So Reliable

Filed by KOSU News in World News.
December 6, 2012

The earthy smell of a fresh beet may spark delicious thoughts for us, but for a fruit fly, that smell screams danger.

Geosmin, a naturally occurring chemical that gives beets, fresh soil and corked wine their distinctive smell, is also cranked out by bacteria deadly to fruit flies. And it turns out that the tiny flies have a direct pathway from nose to brain made just to detect that smell — and avoid the toxic microbes that produce it.

When Bill Hansson, a professor at the Max Planck Institute for Chemical Ecology in Jena, Germany, and his crew blocked the geosmin-detecting pathway in flies, they ate contaminated food and died. With the pathway intact, they steered clear. The fact that the tiny fly is devoting precious neuronal real estate to this shows how important it has been for survival to be able to detect the smell of spoiled food.

“They have one line for their whole nervous system just telling about this,” Hansson tells The Salt. “On their nose they have cells only detecting this. We tested 3,000 compounds and only got a response to geosmin. That’s an amazing specificity.” His article was published in the journal Cell.

This is the first evidence of a special dedicated pathway for food odor, Hansson says. Animals are also very sensitive to smells that are sexual signals. But those are blends of pheromones, rather than a single smell.

People don’t have a dedicated pathway to detect geosmin. That may be because those microbes don’t pose a threat to us. Also, humans have many times more smell receptors than fruit flies. And we eat a much broader range of foods. Some of us even like beets.

In fact, geosmin can be a pleasant smell: Think about a farmer’s field being plowed in the spring, or the garden just after it rains. But it’s also responsible for the funky smell that sometimes troubles municipal water systems. (Supertasters may be able to smell germs in their sinuses, according to a recent study, but most of us don’t have that talent.)

But the poor grad student who worked with the flies picked up a moldy geosmin stink that followed him around the laboratory. “It really doesn’t smell nice,” Hansson said. “You can smell him down the corridor.”

There’s no question that humans and other mammals react strongly to the smell of spoiled food. Just opening the office refrigerator is usually enough to prompt an “ugh!” or sometimes worse. But unfortunately, people don’t have the ability to recognize the smell of dangerous bugs like E. coli or salmonella.

Still, this research could prove useful to humans. If dedicated smell pathways like the fruit fly’s geosmin detector could be found in insects that pose a threat to humans — mosquitoes, say, or agricultural pests like the corn borer — Hansson thinks they could be used to develop repellents that would be safer than pesticides.

What smell screams danger to Hansson? Not geosmin, but the smell of vomit. Hansson remembers a long car trip in his native Sweden. His young son threw up in the back seat. Hansson found the hours spent smelling even the faintest remains of that smell to be excruciating. “It’s such a strong stimulus. And it’s one we don’t adapt to. It’s telling us someone has eaten something that made them sick. That’s an important evolutionary signal.” [Copyright 2012 National Public Radio]

Leave a Reply

9PM to 5AM The Spy

The Spy

An eclectic mix of the Spy's library of more than 10,000 songs curated by Ferris O'Brien.

Listen Live Now!

5AM to 9AM Morning Edition

Morning Edition

For more than two decades, NPR's Morning Edition has prepared listeners for the day ahead with two hours of up-to-the-minute news, background analysis, commentary, and coverage of arts and sports.

View the program guide!

9AM to 10AM The Takeaway

The Takeaway

A fresh alternative in morning news, "The Takeaway" provides a breadth and depth of world, national and regional news coverage that is unprecedented in public media.

View the program guide!

Upcoming Events in your area (Submit your event today!)

Streaming audio and podcasts

Stream KOSU on your smartphone

Phone Streaming

SmartPhone listening options on this page are intended for many iPhones, Blackberries, etc. with low-cost software applications available to listen to our full-time web streams, both News on KOSU-1 and Classical on KOSU-2.

Learn more about our complete range of streaming services

We're perfecting the patient experience - Stillwater Medical Center