Production and characterization of partially purified extracellular thermostable α-amylase by Bacillus subtilis in submerged fermentation (SmF).

A Bacillus strain was isolated from soil samples from the campus area of Dicle University. Based on 16S ribosomal RNA sequencing, the microorganism was closely related to Bacillus subtilis. Effects of different culture medium, incubation time, carbon and nitrogen sources, and various starches, flours, and chemicals on α-amylase production were examined. Maximum enzyme production (7516 U/mL) was obtained in a basal medium A containing 0.05% Tween 40 in 24 h. Partially purified enzyme showed maximum activity at 60 °C with an optimum pH of 6.0. The effects of 0.2% detergents (sodium dodecyl sulfate [SDS], CHAPS [3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate], and commercial detergent Omo Matic) on partially purified enzyme activity over a period of time (15-150 min) were examined and the order of inhibition effect from the most to the least was found as SDS > Omo Matic > CHAPS. Different metal ions inhibited α-amylase activity at low concentrations (1.5 mM). Co²⁺ was a mild inhibitor and Hg²⁺ and Cd²⁺ were potent inhibitors, whereas Ca²⁺ and Mg²⁺ increased the enzyme activity. At 20 mM, Ca²⁺ enhanced enzyme activity, and different Ca²⁺ concentrations (10-300 mM) were studied.