Protease production by thermophilic Bacillus sp strain SMIA-2 cultivated in liquid cultures containing 1% maltose as a carbon source and supplemented with whey protein (0.1%) and corn steep liquor (0.3%) reached a maximum at 14 h, with levels of 42 U/mg protein. The microorganism was capable of utilizing a wide range of carbon sources, but protease activity varied according the carbon source. Starch and maltose were the best carbon sources in the present study for protease secretion, while lactose and sucrose were less effective. Increasing maltose concentration in the medium until 1%, improved the growth of the organism and the enzyme activity. Regarding the amounts of corn steep liquor and whey protein in the medium, the concentrations of 0.2% and 0.1% respectively, were considered the most effective for protease secretion by the organism. Studies on the protease characterization revealed that the optimum temperature of this enzyme was 70ºC. Thermostability profile indicated that the enzyme retained 80% of the original activity after 2 h heat treatment at 60ºC. At 70ºC, 70% of the original activity was retained after 15 min heat treatment. The optimum pH of the enzyme was found to be 8.5. After incubation of crude enzyme solution at room temperature for 2 h at pH 6.0-10.0, a decreased of about 15% of its original activity at pH 8.5 was observed. At pH 10.0, the decrease was 24%. In the presence of 1.0 M and 5.0 M NaCl, 76% and 37% of protease activity was retained after 2 h incubating at 45ºC respectively.
protease; thermophilic bacterium; Bacillus sp
