Characterization of a salt-tolerant extracellular a-amylase from Bacillus dipsosauri.

Abstract

The aims of this study were to purify and characterize an extracellular alpha-amylase from the salt-tolerant bacterium Bacillus dipsosauri. An extracellular alpha-amylase from B. dipsosauri strain DD1 was studied using the synthetic substrate 2-chloro-4-nitrophenyl-alpha-D-maltotrioside. Formation of the enzyme was induced by starch, repressed by D-glucose and highest after growth in medium containing 1.0 mol l-1 KCl. The alpha-amylase activity increased with KCl concentration, showed a pH optimum of 6.5, was stable up to 60 degrees C and was stimulated by 1.0 mol l-1 Na2SO4. The enzyme was purified from spent culture medium to apparent homogeneity by precipitation with ethanol, ion-exchange chromatography on DEAE-cellulose, centrifugal membrane filtration and gel-filtration chromatography on BioGel P-100. The purified enzyme had a denatured molecular mass of about 80 kDa but behaved on non-denaturing polyacrylamide gels as if it had a mass of about 30 kDa. The enzyme was partially inhibited by glucose-containing oligosaccharides of increasing length and strongly inhibited by the divalent cations Cd2+ and Zn2+. The extracellular alpha-amylase from B. dipsosauri strain DD1 was purified to homogeneity and found to exhibit an unusually high degree of salt tolerance. The alpha-amylase from B. dipsosauri differs from previously described enzymes and may be useful for the processing of starches under high-salt conditions.