Abstract: The study aimed to optimize the fermentation process of Bacillus thuringiensis NBIN-863.The key factors of the media components were investigated by using Plackett-Burman (PB) design.The central axises of these factors were determined by using steepest-ascent method.The optimized medium for Bacillus thuringiensis NBIN-863 was determined by central combination design and response surface method.It demonstrated that the key factors in NBIN-863 fermentation broth were starch and soybean meal.The optimized medium was obtained through response surface analysis as35.2 g/L of starch,34.7 g/L of soybean meal.The crystal conte nt of NBIN-863 fermentation broth was measured as5.4 mg/mL.The fatality rate of NBIN-863 fermentation broth for nematodes was81.0%,which was very close to the predicted value (81.2%) and80% higher than the actual mortality rate (45.0%) of NBIN-863 before optimization.

Key words: nematodes, Bacillus thuringiensis, response surface method, mortality rate