Abstract:

An obligate alkaliphilic Bacillus strain was isolated from a soil sample and identified as Bacillus cohnii APT5 based upon phylogenetic and phenotypic analyses. The optimum growth pH of B. cohnii APT5 was 10.0. B. cohnii APT5 was also found capable of producing an extracellular alkaline protease that showed optimum activity (693,318 U/min) at 50 °C and pH 11.0 when grown in a medium containing casein. The enzyme was partially purified 3.22-fold with a yield of 78.74% after acetone precipitation and cation exchange column chromatography, respectively. The partially purified enzyme maintained its activity when incubated at 50 °C for 2 h. It was stable at pH 11.0 at room temperature for 72 h. Furthermore, the alkaline protease activity was not completely inactivated by the specific inhibitors of serine alkaline proteases and metalloproteases such as PMSF and EDTA. While 1 mM PMSF had no effect on the enzyme activity, a 10 mM concentration of PMSF slightly decreased the activity, producing a relative activity of 76%. In addition, the enzyme was found to be very stable toward surface active agents such as SDS, Tween 20, Tween 80, and Triton X-100. None of the metal ions used (Ca2+, Mg2+, Zn2+, Fe2+, and Mn2+) showed an inhibitory effect on enzyme activity. On the contrary, APT5 alkaline protease activity increased 53% when treated with Mn+2. It was concluded that the active center of APT5 alkaline protease required Mn+2 as a cofactor. Based on the thermostability, pH stability, and resistance of B. cohnii APT5 alkaline protease against inhibitors, this enzyme may be very useful in commercial applications, particularly in the detergent industry.

Keywords: