Biodegradation of lignin and hemicelluloses

Abstract

The compositions and percentages of lignin and hemicellulose vary from one plant species to another so it is difficult to arrive at generalizations concerning structure and abundance of these polymers. Moreover, composition varies within a single plant (roots, stems, leaves), with age (heartwood versus sapwood), stage of growth (early wood versus late wood in annual rings) and with the conditions under which the plant grows. Study over many decades has elucidated the major structural features of wood hemicelluloses and lignins, along with the biochemical mechanisms for their degradation. These have been the subjects of comprehensive book-length reviews (e.g. Higuchi 1985a). More specifically, the structures (Fengel and Wegner 1984) and degradation (Shoemaker 1990; Higuchi 1990; Kirk and Farrell 1987; Reiser et al. 1989; Leisola and Garcia 1989) of lignin have been the subject of several reviews, as have the structures (Aspinall 1959; Tlmell 1964, 1965; Wilkie 1979; Lewis and Paice 1989) and degradation (Dekker and Richards 1976; Reilly 1981; Zimmerman 1989; Dekker 1985; Woodward 1984; Biely 1985; Wong et al. 1988; Johnson et al. 1989) of hemicellulose components. Most recently, attention has turned to the molecular characteristics of these enzymes (Gilkes et al. 1991; Kersten and Cullen 1992). It is beyond the scope of the present review to recapitulate these findings in detail. Rather, the focus will be on specialized or recently revealed aspects.