Molecular Biology of Xylan Utilization by Thermoanaerobes

Xylans are linear polymers possessing a β-1,4-linked D-xylose backbone with branches containing 4-O-methyl D-glucuronic acid and l-arabinose. In several types of wood, particularly hardwoods, some of the sugar residues are acetylated (see Figure 33.1 for the schematic representation of the structure). Xylans or hemicelluloses are the second most abundant type of polysaccharides, after cellulose, in nature. As components of plant cell walls they constitute as much as 40% of all plant biomass (Timell, 1967; Aspinall, 1980; Gong et al., 1981). It is not surprising, therefore, that they are an attractive source of carbon and energy for microbes living in natural soil and aquatic habitats and that microorganisms have developed efficient ways to degrade these polymers and use their components.