Fungus foils polymer that defeats recycling

A common tree-rotting fungus is the first to biodegrade an otherwise impervious resin found in plywood and fiberboard.

WHITE KNIGHT. The white-rot fungus Phanerochaete chrysosporium—the white fuzz on these wood chips—can break down phenolic resin, which is found in products such as plywood and fiberboard. Gusse

White-rot fungi strains leave behind wood’s white cellulose as they break down lignin, the natural polymer that binds cellulose fibers together. The fungal enzymes that degrade lignin, called ligninases, have previously shown promise in chewing up environmental pollutants including polychlorinated biphenyls (PCBs), dioxins, and DDT.

Adam C. Gusse and his colleagues at the University of Wisconsin–La Crosse suspected that the fungi might also be able to break down phenolic resin, a widely used polymer composed of phenol and formaldehyde. The resin makes materials difficult to degrade or recycle, so they usually end up in landfills.

The researchers placed millimeter-size fragments of phenolic resin on culture plates containing any one of five species of white-rot fungi. After 3 days, plates holding the whitish Phanerochaete chrysosporium species turned pink, an indication that some proportion of the brown resin bits had degraded into their basic units, which are pink.

“It was blatantly obvious there was something going on,” says Gusse, now at the University of Wisconsin–Madison.

After 28 days of the resin’s exposure to the fungus, scanning electron micrographs revealed pockmarks on the surface of the resin, the researchers report in the July 1 Environmental Science & Technology.

The team also labeled phenolic resin samples with a heavy carbon atom and subsequently found this atom in the fungus’ culture medium—another sign that P. chrysosporium had broken down the polymer.

The next step, Gusse says, is to investigate whether the ligninases are responsible for the degradation or whether a different mechanism is at work.

Aimee Cunningham is the biomedical writer. She has a master’s degree in science journalism from New York University.

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