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U. scientists unearth the sweet smell of soil

The next time you're digging in your garden, marveling at the sweet smell of Mother Earth, you may want to think of a team of Brown chemists who recently determined how the warm, slightly metallic smell of fresh soil is produced. In a paper published this month in Nature Chemical Biology, Professor of Chemistry David Cane, Jiaoyang Jiang GS and Xiaofei He PhD'07 describe the chemical enzyme that produces geosmin, the compound responsible for the sweet scent of soil.

Geosmin, which is Greek for "earth smell," was identified by scientists more than 100 years ago. But it was only recently that chemists began to understand the chemical enzyme that creates this compound, which is responsible for both the aroma of soil and the earthy taste in drinking water. In soil, geosmin is produced by bacteria; in water, blue-green algae make it. More than two years ago, He, working in Cane's lab, discovered that geosmin was being produced when she was working with an enzyme now known as germacradienol-geosmin synthase.

"We didn't find what we started out to find, but actually found things that were even more interesting than expected," Cane said. Cane and Jiang were surprised to discover that a single enzyme present in both the bacteria and the algae was responsible for the creation of geosmin, and in their latest paper, they outlined the precise process by which geosmin is made in nature.

"We didn't start out to say how geosmin was made, but by sharing information with other laboratories and conducting experiments, we were able to find out how it really works. We discovered something that we didn't initially expect at all," Cane said.

Cane and Jiang's discovery has scientists in other fields talking, too. The research team is currently collaborating with a water purification facility in Australia, where microbiologists hope that by understanding the process by which this smelly substance is made, they can work to block its production in water.

Under certain environmental conditions, the amount of blue-green algae in water can skyrocket, causing geosmin levels to rise. Though the presence of geosmin is harmless to humans, understanding how the compound is produced may help microbiologists develop better ways to both detect and eliminate its scent.

Vintners may also be interested in developing ways of keeping geosmin out of their wine, Cane said.

"The more organisms one finds that make geosmin, the more we realize how important this compound turns out to be. This is a puzzle now that moves into other areas of science," Cane said.

According to Cane, some scientists theorize that the scent of geosmin helps organisms such as marine eels find landmasses that they might otherwise be unable to detect, which can be crucial for these organisms during spawning.

"It has also been suggested that the smell of geosmin in water helps camels locate oases," Cane said. This is also beneficial to the blue-green algae living in these bodies of water, as the camels can pick up spores and carry them to new locations, helping to propagate the species.

"When we get results like these, they're always a bit unexpected. Generating new questions makes us work to probe further and further," Jiang said.

Cane, who is most interested in the pure science aspects of the discovery, is excited about the implications of understanding the process by which geosmin is made.

"The enzyme is no longer a black box, where you put something in, get something out and have no idea of the process that went on inside," he said. "If you can begin to find out what each component is, you can shine a light on the process that takes it from the original to the final product."

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