Characterization of a new Bacillus stearothermophilus isolate: a highly thermostable ?-amylase-producing strain

Abstract

A novel strain of Bacillus stearothermophilus was isolated from samples of a potato-processing industry. Compared to known α-amylases from other B. stearothermophilus strains, the isolate was found to produce a highly thermostable α-amylase. The half-time of inactivation of this α-amylase was 5.1 h at 80°C and 2.4 h at 90°C. The temperature optimum for activity of the α-amylase was 70°C; the pH optimum for activity was relatively low, in the range 5.5–6.0. α-Amylase synthesis was regulated by induction and repression mechanisms. An inverse relationship was found between growth rate and α-amylase production. Low starch concentrations and low growth temperatures were favourable for enzyme production by the organism. At the optimal temperature for growth, 65°C, the α-amylase was a growth-associated enzyme. The optimal temperature for α-amylase production, however, was 40°C, with α-amylase increasing from 3.9 units (U)/ml to 143 U/ml when lowering the growth temperature from 65°C to 40°C. Maximal α-amylase production in a batch fermentor run at 65°C was 102 U/ml, which was 26-fold higher than in erlenmeyer flasks at 65°C. The dissolved O2 concentration was found to be a critical factor in production of the α-amylase.