Cellulose, a principle component of all plant materials, is considered one of the most abundant renewable resources in the world. An estimated synthesis rate of cellulose is approximately 4 X 1010 tones per year. Although it is the most promising renewable energy source to overcome the problems of energy resource, chemicals and food in the future, its enormous potential was recognized only after the cellulose degrading enzymes or cellulases had been identified (Cen and Xia, 1999).
Cellulose is made of linked glucose molecules connected by β-1, 4 bonds (Fig.1.). Cellulose is regarded as a valuable resource largely because it can be decomposed into soluble cellobiose and glucose sugars when β bonds are broken (Dorland's Illustrated Medical Dictionary, 2003). This process is called cellulose hydrolysis. Cellulose hydrolysis occurs naturally in soils, sediments, aquatic environments, and in the digestive tracts