Characterization of extracellular cellulose-degrading enzymes from Bacillus thuringiensis strains

Abstract

The gram-positive spore-forming bacteria, Bacillus thuringiensis (Bt) strains produced novel cellulases which could liberate glucose from soluble cellulose, carboxymethyl cellulose (CMC), and insoluble crystalline cellulose. The maximal cellulase activities were obtained after 60 hrs incubation at 28°C in a LB broth medium with 1% CMC. Maximum CMCase activities were got at 40°C and pH 4.0, respectively, and more than 50% of its maximal activity was retained at 40-60°C for 1 hr, while approximately 40% of its maximal activity was also retained after incubating at 70°C for 1 hr. Most metal ions and reagents such as Ca2+, Mg2+, Cd2+, Pb2+, Zn2+, Cu2+, EDTA, and SDS inhibited the enzyme activities, but K+ and Mn2+ activated the activities. The enzymes from Bacillus thuringiensis strains could be applied in bioconversion of lignocellulosic biomass into fermentable sugars.