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

Abstract

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 H 2O 2 via O 2 − and reduced H 2O 2 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.