Brown-Rot Fungal Degradation of Wood: Our Evolving View

摘要

This overview focuses on fungal attack and degradation of wood by the brown rot fungi. These fungi are perhaps the most important agents involved in the degradation of wood products and in the degradation of dead wood in coniferous ecosystems. In the decay process, brown rot fungi actively metabolize the carbohydrate fraction as well as a more minor portion of lignin, leaving behind a chemically modified lignin residue. The wood loses strength very rapidly in the early stages of degradation because of the rapid depolymerization of the cellulosic fraction. More heavily degraded wood typically displays a cubical, crumbly, brown appearance with little residual strength. Mechanisms employed by brown rot fungi in the biodegradation of wood are both enzymatic and non-enzymatic. These fungi produce no lignin degrading enzymes, but they do have a mechanism that results in lignin modification and slow lignin depletion from wood undergoing decay. Recent work by several groups has suggested that non-enzymatic, low molecular agents produced by the brown rot fungi are responsible for early stages of wood cell wall depolymerization through the production of free radical species. Similarities and differences between brown rot fungi, white rot fungi, and molds are discussed with regard to pH contorl in wood, oxalate production, and metal metabolism. Development of several hypotheses for low molecular weight metabolite function and systems postulated for non-enzymatic degradative activities are reviewed.