Microbial proteases are important group of enzymes that are widely used in pharmaceutical, food agriculture industries and bioremediation process. Present study aimed to isolate a new source of protease producing Bacillus and increase the enzyme produced by optimization of some culture conditions. Obtained results revealed that out of 153 bacterial isolates, only 30 of them were preliminary identified as Bacillus sp.. Bacillus S6-3 was the most potent isolate in protease production, which identified as a strain of Bacillus cereus according to its cultural and morphological characteristics, 16S rRNA gene sequences also confirmed the identification. To increase the protease yield from Bacillus cereus S6-3, some nutritional requirements (skim milk concentration, type of sugar and K2HPO4 concentration) and some environmental conditions (pH level, incubation temperature degree and inoculum size) were investigated. Obtained results showed that the optimum parameters for maximum protease production (327.32 U/ml) by Bacillus cereus S6-3 were 6.0 g/L skim milk,10.0 g/L fructose, 0.5 g/L K2HPO4, 1.0 g/L yeast extract, 1.0 g/L MgSO4. 7H2O, 5.0 g/L KCl, 0.2 g/L CaCl2.2H2O, and 5.0 g/L NaCl, initial pH level 6.0, incubation temperature 37 oC, inoculum size (0.5%) and incubation period 48h.
