Purification and characterization of an extracellular esterase from a moderately halophilic bacterium, Halobacillus sp. strain LY5

Abstract

A newly moderate halophilic strain LY5 producing extracellular esterase was isolated and identified. Biochemical and physiological characterization, along with 16S rRNA gene sequence analysis placed the isolate in the genus Halobacillus. Esterase production started from the mid-exponential phase of bacterial growth and reached a maximum level during the mid-stationary phase. The enzyme was highly active against p-nitrophenyl esters with acyl chain lengths from C2 to C10, indicating an esterase activity. Enzyme purification was carried out by combination of 80% ammonium sulphate precipitation, diethylaminoethyl (DEAE)-cellulose ion exchange and Sephacryl S-100 gel filtration chromatography. The molecular weight of the esterase was determined to be 96 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The purified enzyme was highly active over broadranges of temperature (30 to 90°C), pH (6.0 to 12.0) and NaCl concentration (0 to 20%), showing optimal activity at 50°C, pH 10.0 and 10% NaCl. Complete inhibition of the esterase by phenylmethylsulfonyl fluoride (PMSF), phenylarsine oxide (PAO) and diethyl pyrocarbonate (DEPC) indicated that serine, cysteine and histidine residues were essential for its catalytic function. Moreover, it exhibited remarkable stability towards SDS and Triton X-100. Results from the present study indicate that the extracellular esterase from Halobacillus sp. LY5 may have considerable potential for industrial application from the perspectives of its properties. Key words: Moderately halophilic bacterium, esterase, purification and characterization, Halobacillus.