Abstract:The biomass of Bacillus cereus has an important effect on its biological function. In order to increase the yield and spore rate of Bacillus cereus, the optimum carbon and nitrogen source were screened by single factor experiment. The optimal carbon source was 1∶1(mass ratio) mixed glucose and water-soluble starch, and the optimal nitrogen source was 1∶1(mass ratio) mixed soybean peptone and yeast extract. The effects of feeding method, pH, stirring speed and ventilatory capacity on the biomass and spore rate were studied in a 7 L bioreactor. The optimal fermentation conditions were as follows: in 0~9 h, the stirring speed, aeration ratio and pH were 250 r/min, 3 L/min and 6.5, respectively; in 9~18 h, the stirring speed and ventilatory capacity were 350 r/min and 4.5 L/min, respectively and the concentrated medium was added at a flow rate of 0.45 mL/min; at 18 h, the stirring speed, ventilatory capacity and pH were changed to 150 r/min, 2.25 L/min and 7.5 respectively, and the feeding was stopped till the end of fermentation. Based on the above fermentation strategies, the number of viable Bacillus cereus reached 2.2×1010 CFU/mL at 18 h, which was 4.88 times of that before the optimization. At the end of fermentation, the spore rate was over 90%. This study provided basis for the industrial applications of Bacillus cereus.
