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Fungus degrades toxic chemicals.

Fungus degrades toxic chemicals

A fungus that rots fallen trees will reduce to carbon dioxide such persistent environmental poisons as DDT, lindane, PCBs, benzo[a]pyrene and dioxins, say biochemists at Michigan State University (MSU) in East Lansing.

Their report, published in the June 21 SCIENCE, describes the experimental growth of a white rot fungus in glucose solutions containing different organohalides --carbon-containing compounds with attached chlorine or bromine atoms. These chemicals, which include many environmental pollutants, resist degradation by most organisms. Some, like DDT, tend to accumulate in the bodies of animals high on the food chain.

The Environmental Protection Agency (EPA), which funded the study, says it is "guardedly optimistic' about the results. The MSU researchers and the EPA hope the fungus can one day be used to help clean up soils contaminated with toxic chemicals.

The fungus, Phanerochaete chrysosporium, normally lives off the cellulose in wood. The cell walls of wood are protected by lignin, a highly complex ring polysaccharide. Most organisms are incapable of breaking down the lignin to get through to the more digestible cell wall and cell contents, but the white rot fungus possesses an enzyme system that can.

The fungus is thought to break down the lignin by a free-radical mechanism, says John A. Bumpus, one of the paper's authors and a visiting assistant professor at MSU. Free radicals are atoms each with an unpaired electron. They are typically very reactive and nonspecific, attacking a variety of structures. It was the enzyme system's lack of specificity that suggested to Steven D. Aust, professor of biochemistry at MSU, that the fungus might well degrade organohalides as well as lignin.

Aust, Bumpus and two students, Ming Tien and David Wright, labeled the carbon rings of the organohalides with carbon-14, which is mildly radioactive. They then estimated these compounds' rates of degration in fungus-infected glucose solutions by measuring the rate of carbon-14-labeled carbon dioxide produced. After 30 days, 1 to 15 percent of the organohalides had degraded to carbon dioxide. Greater amounts were partially degraded. In the case of DDT, after 18 more days and the addition of more glucose, only 10 percent of the original amount remained, although not all of the other 90 percent had yet been reduced to carbon dioxide.

The fungus's actual usefulness remains to be determined. "It's a long jump from the laboratory to applications in the field,' Bumpus says. "We're optimistic, but we recognize that there may be a lot of roadblocks.'
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Title Annotation:white rot fungus
Author:Dusheck, Jennie
Publication:Science News
Date:Jun 22, 1985
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