Abstract

Protease-producing bacterium Bacillus cereus SU12 was isolated from oysterSaccostrea cucullata. Fifteen strains of bacteria were isolated from oyster S. cucullata and screened for secretion of protease on casein agar plates. Among them, SU12 isolate was selected due to its high enzyme production capacity and was identified as B. cereus SU12 on the basis of its morphological, biochemical and 16S rDNA properties. Media and cultivation conditions were studied to optimize bacterial growth and protease production which includes different carbon and nitrogen sources, in addition to different factors such as incubation time, pH, temperature, NaCl concentrations. At pH 7, temperature 40°C and 2.5% NaCl concentration, carbon source such as starch and beef extract as nitrogen source, the protease activity was maximum. Extracellular protease was isolated, purified to 8.73 fold by diethyl aminoethyl (DEAE) ion-exchange chromatography and its specific activity was determined to be 886.56 U/mg and the sodium dodecyl sulfate poly-acrylamide gel electrophoresis (SDS-PAGE) showed a single band for the purified enzyme, with an apparent molecular weight of 66 kDa. These findings suggest that the scope for the use of B. cereus SU12 strain as suited organism for the industrial production of the extracellular protease enzyme.

Key words: Protease, Bacillus cereus SU12, Oyster, diethyl aminoethyl (DEAE) ion-exchange chromatography, optimization.

Abbreviation

PCR, Polymerase chain reaction; BLAST, Basic Local Alignment Search Tool; NCBI, National Centre for Biotechnological Information; SDS-PAGE,sodium dodecyl sulfate polyacrylamide gel electrophoresis.