Optimization of fermentation medium compositions from dewatered wastewater sludge of beer manufactory for Bacilus thuringiensis delta endotoxin production

摘要

Optimization of medium compositions from dewatered wastewater sludge of beer manufactory for delta endotoxin production by Bacillus thuringiensis was investigated in flask fermentation. Its composition consisted of wastewater sludge hydrolysis broth with several agricultural byproducts (rice bran, soybean meal, corn flour) and mineral salts (MgSO_4.7H_2O; K_2HPO_4; KH_2PO_4; MnSO_4; CaCl_2; NaCl). Rice bran and MgSO_4.7H_2O, CaCl_2 were all found to have a significant influence on delta endotoxin production. The optimal concentration of these three factors were then sequentially investigated using the response surface methodology with a central composite design. The resulting optimal medium components for delta endotoxin production were determined as follows: WWS (20 g/l, dry weight), CaCl_2 (0.3 g/l), MgSO_4.7H_2O (0.32 g/l), and rice bran (5.8 g/l). Using this optimized fermentation media, the yield of delta endotoxin was increased by 34% to 565 mg/l compared with unoptimal medium. Viable cell and spore counts obtained in optimum fermented broth were 1.25×10~9 CFU/ml, 1.07×10~9 CFU/ml, respectively. The LC50 value of Bacillus thuringiensis serovar isralensis against Culex quinquefasciatus was 0.056 mg/l and there was no significant difference between LC50 value of bacterium grown in the medium.