ABSTRACT
Lignocellulosic biomass is a unique renewable natural resource. The major fraction of this material, typically 35-50%, is cellulose, a polymer of glucose. Cellulose is the most abundant organic compound on earth, and is the main constituent of the cell walls of plants. Hemicellulose, the next largest fraction, is also a polymer of sugars, whose types and distributions vary depending upon the particular biomass source. For many types of lignocellulosic material, xylan, a polymer of xylose, represents the predominant fraction of the hemicellulose component. The third largest fraction of lignocellulosic biomass, about 15 to 25%, is typically lignin, a phenylpropane polymer of complex composition (Wyman, 1994). Thus the degradation of lignocellulosic biomass represents an important part of the carbon cycle within the biosphere. Apart from its special significance in the biological carbon cycle, it has a great potential as an alternative source of fuel, feedstock for the chemical industry (Detroy and Julian, 1984; Kuhad and Singh 1993; Wyman, 1994; Zaldivar et al., 2001) and conversion to edible biomass (Nikolov et al., 2000). Lignocelluloses complete utilization would allow self-sustainable processes and products. For these materials, the main processes to which the biotechnological approaches could be of help are the improvement of their digestibility for feeding animals, the mushroom production, the energy sector (alcohol, methane etc), the retting of textile fibres, the biodegradation of toxic aromatic molecules resembling lignin (bioremediation), and many aspects concerning the paper pulp preparation (Ramachandran and Sinha, 1993).
