Cellulose Degradation by Fungi

Cellulose and hemicellulose comprise about 50 and 30%, respectively, of the biomass the nature produces through photosynthesis and are by far the most abundant carbon polymers on earth. Lignin and minor amount of ash make up the remainder of the biomass. In addition to that which already exists in natural settings (especially in trees), cellulose/hemicellulose is a large component of wastes originating from municipal, agricultural, forestry, and certain industrial sources. Its abundance alone supports the contention that it is a valuable raw material for food production, energy generation, and chemical feedstock. Although only a small portion of what the nature produces is presently converted into useful products, this picture will likely change in the future, as the world population must ultimately depend on limited renewal resources for food, energy, and material goods (Millet et al. 1976). Except for directly burning wood and wastes for energy generation, most cellulose-derived products first require degrading of cellulose to constituent sugars before subsequent conversion, usually through microbial fermentation, of the sugars into a wide range of useful products, including ethanol, acetic acid, lactic acid, and antibiotics. Besides generating valuable chemical products, degradation of cellulose also reduces the waste disposal problems associated with landfills and burning forests (Katzen and Monceaux 1995). After several decades of research worldwide, there are two main routes to cellulose degradation: chemical (alkaline or acid) and biological (enzymatic or microbial). Of the latter route, fungi and anaerobic rumen bacteria are excellent candidates. In this chapter, we specifically focus on cellulose degradation by fungi and compare the economics of alternative processes.