Production Of Bacillus Thringiensis Using Organic Wastes As Culture Medium

Bacillus thuringiensis(Bt.) is an important biological insecticide and widely applied all over the world.However,conventional culture medium such as soybean meal for Bt production constitutes 30%～40%of total production cost.It is most important to seek an alternative cost-efficient culture medium.Thus,the purposes of the present study are to explore the possibility of common organic wastes acted as culture medium for Bt production in order to provide a new approach to harvest Bt as well as treat and dispose organic wastesBacillus thringiensis 546 was used in this study.A varity of orgianic wastes including animal hair,biogas anaerically digested liquid and sewage sludge were selected as alternative culture medium,in which animal hair was hydrolyted before it was used as culture medium.The results showed that the number of viable cells in the hair hydrolyte medium was 5.00×10~8cells/mL at 48 hours for fermention,exhibiting a little lower than that in the soybean meal medium with 1.00～5.00×10~9cells/mL.But the number of viable cells in anaerically digested liquid for biogas unexpectedly reached 2.00～7.00×10~9 cells/mL.The numbers of viable cells in the sewage sludge medium with 1.0×10~9cells/mL were similar to that obtained from the soybean meal medium.The mediums using anaerically digested liquid for biogas and sewage sludge could produce 1.00～4.00×10~9 cells/mL and 1.0～2.0×10~8cells/mL of Bacillus thringiensis spores, respectively,which was similar to that obtained from the conventional soybean meal medium.However,1.0～2.0×10~8cells/mL of Bacillus thringiensis spores harvested from the hair hydrolyte medium was a bit lower than that obtained from the conventional soybean meal medium with 7.00×10~8～3.00×10~9cells/mL.It was noted that the rate of sporulation fermented in the hydrolyte and anaerically digested liquid for biogas was 6 hours earlier than that in the conventional soybean meal medium.Sporulation appearence in sewage sludge medium was 10 hours earlier than that in the conventional soybean meal medium.Higher entomotoxicity of Bt obtained from the hair hydrolyte,methane-generating anaerobical liquid,and sewage sludg mediums in compared to soybean meal medium was observed using the Helicoverpa armigera as a worm ofbioassay.The crystal protein yield was measuresed at the end of fermentation of Bacillus thringiensis.It was found that the crystal protein yield obtained from the sewage sludg medium was the highest.Optimum fermentmental parameters for Bt in sewage sludge medimum were:2.0%～2.5%of sewage sludge solid content,pH7.0 for initial phase in medium,30℃for medium temperatiure,and 36h for reaction time.Under the above condition,the number of viable cells and spores of Bacillus thringiensis were 8.2×10~9cells/mL and 3.5×10~9 cells/mL,respectively.Bt protein introduced into the soil could be adsorbed by soil particles by which it could resist the attack of soil microorganisms.The adsorption of toxic protein on the selected soil reached saturation when the addition of the toxic protein was 1.0 mg / mL with the adsorption amount of 0.32 mg / mg.The desorption rate of Bt toxic protein was 12.7%by phosphate buffer solution and 3.2%by NaCl solution.It was found that Bacillus thuringiensis incorporated into the soil still maintained the insecticidal activity.Therefore, possible risk of Bacillus thuringiensis cannot be recluded.