CHARACTERIZATION OF A NEW BACILLUS-STEAROTHERMOPHILUS ISOLATE - A HIGHLY THERMOSTABLE ALPHA-AMYLASE-PRODUCING STRAIN

A novel strain of Bacillus stearothermophilus was isolated from sample s of a potato-processing industry. Compared to known alpha-amylases fr om other B. stearothermophilus strains, the isolate was found to produ ce a highly thermostable alpha-amylase. The half-time of inactivation of this alpha-amylase was 5.1h at 80 degrees C and 2.4 h at 90 degrees C. The temperature optimum for activity of the alpha-amylase was 70 d egrees C; the pH optimum for activity was relatively low, in the range 5.5-6.0. alpha-Amylase synthesis was regulated by induction and repre ssion mechanisms. An inverse relationship was found between growth rat e and alpha-amylase production. Low starch concentrations and low grow th temperatures were favourable for enzyme production by the organism. At the optimal temperature for growth, 65 degrees C, the alpha-amylas e was a growth-associated enzyme. The optimal temperature for alpha-am ylase production, however, was 40 degrees C, with alpha-amylase increa sing from 3.9 units (U)/ml to 143 U/ml when lowering the growth temper ature from 65 degrees C to 40 degrees C. Maximal alpha-amylase product ion in a batch fermenter run at 65 degrees C was 102 U/ml, which was 2 6-fold higher than in erlenmeyer flasks at 65 degrees C. The dissolved O-2 concentration was found to be a critical factor in production of the alpha-amylase.