Characterization of an organic solvent-tolerant α-amylase from a halophilic isolate, Thalassobacillus sp LY18

A halophilic isolate Thalassobacillus sp. LY18 producing extracellular amylase was isolated from the saline soil of Yuncheng Salt Lake, China. Production of the enzyme was synchronized with bacterial growth and reached a maximum level during the early stationary phase. The amylase was purified to homogeneity with a molecular mass of 31 kDa. Major products of soluble starch hydrolysis were maltose and maltotriose, indicating an alpha-amylase activity. Optimal enzyme activity was found to be at 70A degrees C, pH 9.0, and 10 % NaCl. The alpha-amylase was highly stable over broad temperature (30-90A degrees C), pH (6.0-12.0), and NaCl concentration (0-20 %) ranges, showing excellent thermostable, alkalistable, and halotolerant nature. The enzyme was stimulated by Ca2+, but greatly inhibited by EDTA, indicating it was a metalloenzyme. Complete inhibition by diethyl pyrocarbonate and beta-mercaptoethanol revealed that histidine residue and disulfide bond were essential for enzyme catalysis. The surfactants tested had no significant effects on the amylase activity. Furthermore, it showed high activity and stability in the presence of water-insoluble organic solvents with log P (ow) a parts per thousand yenaEuro parts per thousand 2.13.