Optimization of Medium Compositions Using Statistical Experimental Design to Produce Lipase by Bacillus subtilis

S. Cheng, Y. Wang and F. Liu

Abstract
Statistical experimental design was employed to optimize medium compositions to enhance the activity of lipase from Bacillus subtilis. Plackett–Burman design was applied to evaluate the effect of different medium compositions obtained by one-factor- at-a-time experiments, and ammonium chloride, ammonium sulfate and dipotassium hydrogen phosphate were found to influence the activity of lipase significantly. Steepest ascent method was employed to approach the experimental design space, followed by an application of central composite design and response surface methodology for further optimization. A quadratic model was found to fit the lipase activity, and the optimal medium compositions were determined as included 45 g L–1 NH4Cl, 20.4 g L–1 (NH4)2SO4 and 12.6 g L–1 K2HPO4. The corresponding lipase activity was 91.39 U mL–1. Validation experiments were also carried out to prove the adequacy and the accuracy of the model obtained. The lipase activity reached 91.46 U mL–1, which was almost equal to the actual predicted value, about 4.94-fold increase compared with that using the original medium.

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Keywords
Bacillus subtilis, central composite design, lipase, Plackett–Burman design, response surface methodology