Characterization of cellulases from thermophilic bacilli and their application for the saccharification of sugarcane bagasse

摘要

Cellulases from thermophilic bacteria are likely to be more stable and are required in countless biotechnological applications. Bacillus being a house of thermostable proteins has frequently been studied for the production of cellulases. During the process of composting, distinct temperature changes are observed including significant rise that favors the growth of thermophiles with the ability to degrade plant based waste materials. Therefore, isolation of bacterial strains was carried out from a composting site; screening of the isolates revealed capability of three of the isolates, MAH14, MAH66 and MAH80, to produce endoglucanase (EG) and b-glucosidase (BGL) at 50°C. On the basis of biochemical characters MAH66 and MAH80 were identified as the strains of Bacillus licheniformis whereas, MAH14 was identified as Bacillus subtilis . The cellulase preparations from these bacteria were studied for their thermostability by investigating the half-life (t 1/2 ) and melting temperature (T m ). The MAH80 cellulase exhibited more stability with a T m of 60°C and a t 1/2 of 70 min at 50°C.The prospected application of cellulase crude preparation from the strains was estimated by carrying out experiments on the saccharification of untreated and alkali-treated sugarcane bagasse (SB) and the data was compared with the saccharificaiton of CMC. Hydrolysis rate from MAH14 of untreated SB was higher as compared to alkali pretreated SB and CMC. The amount of reducing sugars liberated by the action of cellulase preparation from MAH 66 on untreated SB (1.7 mg mL -1 ) was higher than on alkali treated SB (0.29 mg mL -1 ). While the enzyme from MAH14 yielded almost equal amount of sugars when applied either on alkali treated SB (0.56 mg mL - 1) or on CMC (0.6 mg mL -1 ). Results from this study revealed the capability of indigenous thermophilic bacterial strains for cellulase production and biomass saccharification.