The involvement of extracelluar substances for reducing molecular oxygen to hydroxyl radical and ferric iron to ferrous iron in wood degradation by wood decay fungi

Extracelluar substances that had single-electron oxidation activity were isolated from cultures of brown-rot and white-rot. The molecular weights of the substances estimated by gel-filtration were very small, in a range of 1000-5000. The substances catalyzed a redox reaction between electron donors and O-2 to produce H2O2 via O-2(-) and reduced H2O2 to HO .. Furthermore, the substances reduced Fe(III) to Fe(II) and strongly adsorbed Fe(II). The production of HO . in cultures of brown-rot fungi was directly proportional to the rates in the degradation of wood, crystalline cellulose and lignin-related model compounds in the cultures. Most of the HO . was produced by a redox reaction between O-2 and certain electron donors catalyzed by the low molecular weight substance in Tyromyces palustris cultures. The extent of one-electron oxidation activity of the low molecular weight substance from white-rot basidiomycetes was also correlated with that of the wood-degrading activity, but the phenol oxidase activity was not. (C) 1997 Elsevier Science B.V.