OPTIMIZING PHB AND PROTEASE PRODUCTION BY BOX BEHNKEN DESIGN

Mixed culture is more suitable to adapt more flexible fermentation process and also to produce different product simultaneously. In this study, a mixed Bacillus culture was investigated for their ability to produce the bioplastic Polyhydroxybutyrate and both of the mesophilic and the thermophilic proteases, in one flask. Box-Behnken experimental design was used in this investigation. The produced amount of PHB has been increased significantly. Meanwhile there is a competition between PHB and proteases. The maximum produced amount of PHB using Box-Behnken design was 2.82 g/l/48 h with protease activity equal to 41.9 Units/ml/48 h for thermophilic proteases and 99.65 Units/ml/48 h for mesophilic proteases. Excel solver was used for extraoptimization for the optimum conditions obtained from Box-Behnken experiments and its model. The maximum PHB obtained after using Excel solver was 2.88 g/l/48 h. The maximum mesophilic and thermophilic activities obtained at the same PHB production conditions were 175.68 and 243.38 Units/ml respectively. The model accuracy obtained from Excel solver was 118.8%, which prove that the power of the experimental design in optimizing such complicated process. The strategies used in this study are recommended for the production of PHB and different proteases simultaneously, using Bacillus mixed culture.