Medium Optimization for Lipopeptide Produced by Bacillus natto TK-1 Using Response Surface Methodology

Response Surface Methodology was applied to optimize the culture components for lipopeptide production by Bacillus natto TK-1. In the first step, two level factorial design of Plackett-Burman was used to evaluate the influence of six related factors. It showed that three factors playing the important roles in the medium, including peptone, yeast extract powder and CaCl_2. The path of steepest ascent was used to approach the optimal region of the fermentation conditions subsequently. In the third step, the concentrations of those three main factors were further optimized by using Box-Behnken and Response Surface Analysis. By solving the quadratic regression model equation, the optimal concentrations of the variables were determined as: peptone 1.73%, yeast extract powder 0.063 %, CaCl_2 1.385×10-4mol/L. Under the optimal culture conditions, the diameter of haemolysis zone increased 29.3 % than before. HPLC analysis showed the precise production of lipopeptide was 30.2% higher than preliminary culture. Furthermore, at three batches cultivation, the experiment values under the optimal conditions agreed with the predictive values. It showed that Response Surface Methodology was proper and a good choice for optimization.