Biochemical Mechanisms for the Biodegradation of Wood

Abstract

The biochemical mechanisms for the biodegradation of wood by white-rot and brown-rot fungi are discussed on the basis of recently reported findings. The white-rot wood decay process comprises the enzymatic hydrolysis of cellulose and oxidative breakdown of lignin; the one-electron oxidation mechanism involved in the initial oxidation of lignin is described. In the enzymatic breakdown of lignin, a cation radical intermediate plays a key role. In the brown-rot wood decay process, cellulose degradation is more critical than that of lignin, and the possible role of Fenton's system, which has been receiving keen attention recently, is discussed in relation to the oxidative breakdown of cellulose. As an alternative hypothesis, however, the possible role of oxalic acid in the hydrolytic cleavage of the cellulose chain is proposed, because oxalic acid is one of the strongest physiological organic acids, and is commonly known as a peculiar secondary metabolite produced by brown-rot fungi.