Physical, chemical and biochemical considerations in the biological degradation of wood

Microbial degradation of wood should be considered on two levels. From an organismic point of view degradation concerns the interaction of the cell with its microenvironment. At this level, degradation is strongly affected by diffusion of the degradative agents and the uptake of the oligomeric products. From a biochemical perspective. degradation concerns the molecular architecture of the biopolymers, the capacities of the enzymatic catalysts to bind to them and the catalytic turnover rates. Lignin reactivity is limited by the accessibility. heterogeneity. and stability of the polymeric linkages; cellulose reactivity is limited mostly by accessibility and crystallinity: and hemicellulose reactivity is limited by substitution. The relationships among wood structure, chemistry and biological decomposition have been reviewed many times in articles and occasionally in complete texts (Nicholas, 1973; Loewus and Runeckles, 1977; Rowell, 1984; Higuchi, 1985). If one also considers the specialized texts and monographs on the structure and degradation of individual wood components such as cellulose (Hajny and Reese, 1969) and lignin (Kirk, et al., 1980; Crawford, 1981; Kirk and Cowling, 1984) and volumes from symposia on biomass conversion (e.g., Wilkie, 1975; Gaden et al., 1976; Ghose, 1978; Hollaender, 1981). it is apparent that one cannot add much new detail to what has previously been said. Such, however, is not the purpose. My intention here is to resynthesize past knowledge with a few major recent findings and to relate tissue and polymer structure of wood to mechanisms for its biological and biochemical degradation.