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

One-electron oxidation activity, as measured by ethylene generation from 2- keto-4-thiomethylbutyric acid, phenol oxidase activity, and the generation of hydroxyl radical were examined in cultures of the lignin-degrading white -rot basidiomycete fungus, Trametes (Coriolus) versicolor. The activity lev els of specific lignin-degrading enzymes and cellulases, as well as the rat e of wood degradation, also were examined. The fungus secreted a low-molecu lar-weight substance (M-r 1000-5000) that catalyzed a redox reaction betwee n molecular oxygen and an electron donor, to produce the hydroxyl radical v ia hydrogen peroxide. During wood decay, T. versicolor also produced signif icant amounts of laccase and lignin peroxidase, carboxymethyl cellulase, an d Avicelase. The roles of the hydroxyl radical, phenol oxidases, and cellul ases in wood degradation by white-rot fungi are discussed. That the hydroxy l radical produced by the low-molecular-weight substance secreted by T. ver sicolor results in new phenolic substructures on the lignin polymer, making it susceptible to attack by laccase or manganese peroxidase is suggested. (C) 1999 Elsevier Science B.V. All rights reserved.