Hydroxyl radical generation by an extracellular low-molecular-weight substance and phenol oxidase activity during wood degradation by the white-rot basidiomycete Phanerochaete chrysosporium

The mechanism of wood degradation by white-rot fungi is not understood in detail other than it is involving phenol oxidases (which are lignin-degrading enzymes) and cellulases. The possible role of hydroxyl radicals in degradation by the white-rot fungus Phanerochaete chrysosporium was studied. The production of a low-molecular-weight substance that is secreted was measured periodically. The substance catalyzes a redox reaction between O-2 and an electron donor producing hydroxyl radicals in the culture fluid of this fungus with glucose or wood as the carbon source. We examined the possible role(s) of one-electron oxidation activity by phenol oxidases and hydroxyl radicals in wood degradation by this fungus. Assays of phenol oxidase activity showed that P. chrysosporium produced much manganese peroxidase in wood culture, and that the activity peaked early in incubation. The generation of hydroxyl radicals in the redox reaction was related to the rate of wood degradation, but the activity of phenol oxidases was not related. Therefore, hydroxyl radicals are important in wood degradation by this fungus.