9 Enzymology and Molecular Genetics of Wood Degradation by White-Rot Fungi

Our purpose in this chapter is to provide an overview of the enzymology and associated molecular genetics of wood decay by white-rot fungi. These fungi are able to fragment the major structural polymers of wood and other lignocellulosics-lignin, cellulose, and hemicelluloses—and to further metabolize the fragments. The whiterot fungi and related litter-degrading fungi are perhaps nature’s major agents for recycling the carbon of lignified tissues; indeed, no other microorganisms have been described that can mineralize fully lignified tissue. The white-rot fungi are obligate aerobes, deriving their nourishment from the biological combustion of wood and associated materials. using molecular oxygen as terminal electron acceptor. Their internal energy-yielding metabolic pathways are those shared by most aerobic organisms. Our focus here is on the extracellular polymer-fragmenting enzyme systems and not on the intracellular fragment-metabolizing machinery. This chapter is meant to provide some insight into the biochemistry and molecular biology of the decay process as it is harnessed in biopulping. We refer to summaries and other literature that can be consulted for further detail on specific aspects of the subject. Brief descriptions of the structure of the wood cell and its component polymers, and of the microscopic features of decay, provide a framework for the description of the enzymology and molecular genetics.