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 28ºC in a LB broth medium with 1% CMC. Maximum CMCase activities were got at 40ºC and pH 4.0, respectively, and more than 50% of its maximal activity was retained at 40-60ºC for 1 hr, while approximately 40% of its maximal activity was also retained after incubating at 70ºC 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.