Genetic master switch sends bacteria toward 'seafo...( Chitin the Earth's second-most abundan...)

Chitin, the Earth's second-most abundant biological material, is a major component in the flurry of skeletal debris discarded daily by crustacean creatures in the world's oceans. If left undisturbed, this tough insoluble material, a cousin to cellulose, would pile up on the ocean's floor and wreak havoc with marine ecosystems. Fortunately, armies of bacteria act as chitin's cleanup crew, and two Johns Hopkins University biologists have made a key discovery about how and when these microscopic soldiers launch their search-and-devour missions.

Writing in the Online Early Edition of "Proceedings of the National Academy of Sciences" for the week of Dec. 29, 2003, Xibing Li and Saul Roseman reported that they had found a genetic master switch that reacts to the presence of nearby chitin and sets off a biological chain reaction, causing the bacterial feast to begin. Understanding this process is important because 10¹¹ tons of chitin (pronounced "KITE-in") are dumped annually in the oceans, largely by tiny sea animals called copepods, which shed their shells as they grow. "If nothing happened to this debris, we'd be up to our eyeballs in chitin, and the carbon and nitrogen cycle upon which marine life depends would be gone within 50 to 75 years," said Roseman, a professor of biology in the Kreiger School of Arts and Sciences at Johns Hopkins.

Researchers were puzzled about the disappearance of chitin because little of the material turned up in sediment on the ocean floors. Where did all of the chitin go? Then, about 70 years ago, two microbiologists determined that bacteria were quickly consuming the sinking shells and preserving the ecological balance. Since then, however, several mysteries have remained: How do the bacteria find these undersea meals? How do these microorganisms attach themselves to the chitin? How do they degrade the tough material and turn it into food?

During the past decade, Roseman and his colleagues have
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Contact: Phil Sneiderman
prs@jhu.edu
443-287-9960
Johns Hopkins University
29-Dec-2003

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