Optimization of production and partial characterization of cellulase and protease enzymes from Aeromonas hydrophila ASM-S32

Abstract

Microbial hydrolytic enzymes, especially cellulase and protease, are widely used in industrial processes due to their low cost, large productivity, chemical stability, environmental protection, plasticity and vast availability. But existing cellulase and protease enzymes are not capable enough to fulfil the industrial demands due to the lack of adapting operational conditions. So, the present study focused on extracting enzymes from microbial sources to overcome the problems. 260 isolated bacterial strains from different areas of Sylhet, Bangladesh, were screened for their cellulolytic and proteolytic activities using Carboxymethylcellulose (CMC) and skim milk agar respectively. Among them 6 cellulolytic and 15 proteolytic bacteria were initially identified. Based on the capability to degrade CMC and skim milk, strain S32 was found to be the most potential among the isolates. Biochemical tests and molecular identification revealed that S32 is a strain of Aeromonas hydrophila and was later named as Aeromonas hydrophila ASM-S32. Maximum cellulase production by the strain A. hydrophila ASM-S32 was obtained after 18 h of incubation in a fermentation medium with an initial pH of 6.5 at 37°C and that was 4-fold higher as compared to unoptimized conditions. Maximum cellulase activity was observed at 60°C with a pH of 6.5 in presence of Ca2+ metal ion. In case of protease, optimum enzyme production was observed after 24 h of incubation with an initial pH of 8.5 at 37°C and protease production was increased by 1.2-folds when optimized conditions were used. Maximum protease activity resulted from pH 6.0, at 70°C and in presence of Cu2+ ion.