Statistical Optimization of Medium Compositions for Alkaline Protease Production by Newly Isolated Bacillus amyloliquefaciens

S. Cheng, Y. Wang and M. Wang

Abstract
The nutritional medium requirement for alkaline protease production was optimized by newly isolated Bacillus amyloliquefaciens B7. The variables significantly influencing the protease activity were screened through one-factor-at-a-time experiments and Plackett–Burman design, by which fructose and yeast extract were identified as the most significant variables. The 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 of the protease production. The protease production was found to increase from 242.45 U mL–1 to 951.49 U mL–1, approx. a 3.92-fold increase compared with that using the original medium. Validation experiments were also carried out to verify the adequacy and accuracy of the model, and the results showed that the predicted value agreed well with the experimental values. 3120.55 U mL–1 of the maximum enzyme activity was obtained by batch cultivations in a 10 L bioreactor.

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Keywords
Alkaline protease, Bacillus amyloliquefaciens, fermentation optimization, medium composition, response surface methodology