Relationship between production of hydroxyl radicals and degradation of wood by the brown-rot fungus, Tyromyces palustris

In cultures of Tyromyces palustris containing glucose or wood as carbon source, we measured changes in production of a low-molecular-weight (1 similar to 5kDa) extracellular substance that catalyzes a redox reaction between O-2 and an electron donor to produce the hydroxyl radicals, OH. We also measured the activity of one-electron oxidation relative to degradation of wood, crystalline cellulose, and lignin substructure models in cultures. In the glucose cultures, activities of two cellulases (CMCase and Avicelase) were negligible, as was production of oxidant. In the wood cultures, CMCase and oxidant production, but not Avicelase activity, were high. These findings suggest that most of the one-electron oxidation in wood cultures is caused by hydroxyl radicals produced in a redox reaction between O-2 and certain electron donors catalyzed by the low-molecular-weight substance. The production of .OH in T. palustris cultures was related to the rates of degradation of wood, crystalline cellulose, and lignin models in the cultures. On the basis of these results, we suggest that the hydroxyl radicals produced in the redox reaction between O-2 and an electron donor, mediated by the low-molecular-weight substance, play an important role in wood and crystalline cellulose degradation by T. palustris.