Optimization of bacteriocin-like substance production by Bacillus cereus XH25 using response surface methodology

Response surface methodology was employed to optimize medium composition of bacteriocin-like substance production by Bacillus cereus XH25. The initial pH of medium, soluble starch and (NH4)(2)SO4 were found to influence significantly on the bacteriocin-like substance production. The steepest ascent method was undertaken to access the optimal region of the above three significant factors and then their concentrations were optimized by the central composite design and the response surface method. The results indicated that the quadratic term of the three factors and the interactions between soluble starch and initial pH value, (NH4)(2)SO4 and initial pH value had a significant effect on the production of bacteriocin-like substance. The optimized medium composition was soluble starch 15.32 g/L, (NH4)(2)SO4 6.02 g/L and initial pH value 6.15 which tamped a 21.69% increase of antibacterial activity against Staphylococcus aureus ATCC 9144 when compared with the original medium. The predicted value 12.76 mm was verified subsequently by validation experiments value 12.90 mm. The excellent correlation between predicted and observed values further confirmed the adequacy and accuracy of the model obtained. The results obtained in current work provided a basis for large scale fermentation of bacteriocin-like substance by B. cereus XH25.