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In this study, we intended to increase mass production of Bacillus subtilis SCD121067 through medium optimization by statistical experimental method. For the seed culture of B. subtilis SCD121067, tryptic soy broth and 15 hours were selected as the basic medium and inoculum age respectively. Final dry cell weight of B. subtilis SCD121067 by basic production medium was 1.56 g/L. First, galactose, yeast extract and potassium phosphate dibasic were selected as carbon, nitrogen and phosphate sources for mass production of B. subtilis SCD121067 by using one factor
at a time method. Second, Plackett-Burman experimental design was used to determine the key factors which are critical to maximizing culture the cell mass by fermentation. According to the result of Plackett-Burman experimental design, key factors was yeast extract and K2HPO. Finally, the response surface methodology was performed to obtain the optimum concentrations of two selected variables. The optimized medium composition was consisted of 20 g/L galactose, 36 g/L yeast extract, 0.41 g/L K2HPO4, 0.25 g/L Na2CO3, 0.4g/L MgSO4 and 0.01g/L CaCl2. Dry cell weight (15.4 g/L) by optimum production medium were increased 10 times,
as compared to these determined with basic production medium. Fermentation conditions were examined for the mass production of B. subtilis. The effect of temperature, agitation speed, pH and aeration rate on the mass production of B. subtilis were also studied in a batch fermenter which was carried out in a 2.5 L bioreactor with a working volume of 1.5 L containing optimized production medium.