Morphological Aspects of Wood Degradation by Fungi and Bacteria

Abstract

The structure and chemical composition of wood have a significant influence on its degradation by microorganisms and the resulting patterns of decay. The type of cell, chemical composition, and cell wall morphology may all govern the effects of enzymes on the woody substrate. Wood is made up largely of cellulose, lignin, and hemicellulose in various proportions (Table 1.1). The lignin content of angiosperms is generally lower than that of gymnosperms. Differences in the major hemicellulose present are reflected in the xylose and mannose content (Table 1.1), which represents glucuronoxylan in hardwoods and galactoglucomannans in softwoods. Large differences in the chemical components exist among various woods (Fengel and Wegener 1983) and the composition of different types of cells within wood may also vary (Saka and Goring 1985). The type of lignin found in hardwoods and softwoods is also different. The basic structural unit of lignin may be substituted in two or three positions; the addition of one methoxyl group to the phenol ring results in a guaiacyl unit, the addition of two methoxyl groups results in a syringyl unit. Hardwoods contain varying ratios of syringyl and guaiacyl types of lignin, whereas conifers have primarily guaicyl lignin (Fengel and Wegener 1983).