Screening, cloning and biochemical characterisation of novel esterases from bacillus sp. associated with the marine sponge aplysina aerophoba

Abstract

Two novel esterases (EstB1 and EstB2) were isolated from a genomic library of Bacillus sp. associated with the marine sponge Aplysina aerophoba. EstB1 shows low identity (26-44 %)with the published hydrolases of the genus Bacillus, whereas EstB2 shows high identity (73-74 %) with the carboxylesterases from B. cereus and B. anthracis. Both esterases were efficiently expressed in Escherichia coli under the control of T7 promoter using the vector pET-22b(+). Recombinant EstB1 was purified in a single step to electrophoretic homogeneity by IMAC. A method for the refolding of inclusion bodies formed by the recombinant EstB2 was established to obtain active enzyme. Substrate specificity of the two enzymes towards pnitrophenyl and methyl esters and the respective kinetic parameters Km and Vmax were determined. The temperature optima of EstB1 and EstB2 were determined to be in the range of 30-50°C and 20-35°C, respectively. The pH optima were found to be in the range of 6.5-7.5 and 6.5-8.0, respectively. Both enzymes showed the highest stability in up to 50 % (v/v) DMSO followed by methanol, ethanol and 2-propanol. The influence of high NaCl and KCl concentrations was tested. The inhibition effect of 10-50 mM Zn2+ and 50 mM Mg2+ and Ca2+ ions was observed for both esterases. 1-5 mM PMSF deactivated the enzymes, whereas β-mercaptoethanol, DTT and EDTA had no effect on the enzymes activity.