New thermostable amylase from Bacillus cohnii US147 with a broad pH applicability.

A new thermophilic bacterial strain identified as Bacillus cohnii US147 was isolated from the southern Tunisian soil. The identification was based on physiological tests and molecular techniques related to the 16S ribosomal ribonucleic acid. The isolated strain produced amylase, which was purified. This amylase had an apparent molecular mass of 30 kDa as estimated by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. Amylase US147 showed K (m) and V (max) values of 0.7 mg/ml and 2.2 U/ml, respectively, with starch as the substrate. The enzyme was active in acid and basic pH and had a maximal activity on starch at pH 9 and 70 degrees C. The enzyme was stable at pH 9 for 72 h and retained half of its activity after incubation at 70 degrees C for 150 min. A partially inhibition (15%, 25%, 23%, 20%, and 22%) was obtained with 1 mM SDS, 1 mM NaBO(3), 1 mM H(2)O(2,) 1 mM Zn(+2), and 5 mM ethylenediamine tetraacetic acid (EDTA), respectively. The amylase recovered its original activity by the addition of 10 mM Ca (2+) to the 5 mM EDTA. These properties indicated a possible use of this amylase in starch saccharification, in detergent, and in other industrial applications.