Study On The Screening Of Spinosad-Producing Strains And Optimization Of Fermentation Medium

Spinosad is secondary metabolite produced by fermentation of Saccharopolyspora spinosa with noticeable insecticidal activity. The most active components of the spinosad family are spinosad A and spinosad D which are macrocyclic lactones antibiotic. They are the most effective agricultural pesticides, and used widely in grain storage and agricultural fields. In this paper, we have selected high spinosad-producing strain using mutation breeding and optimized the fermentation medium. The main results were as follows:1. With two times’NTG mutation, one high spinosad-producing strain was achieved,which was128%higher than the initial strain.2. Effect of ten sorts of solid medium on the growth, colony morphology and producing spores of Saccharopolyspora spinosa were investigated. Five sorts of solid mediums were determined according to their growth rate and result of producing spores. On the basis of the above solid medium, the optimal solid medium was chosen through preservation tests at4degree centigrade, which did not cause strain variations in a short time. The optimum medium was as following:Enzyme-hydrolyzed casein0.2%, Yeast extract0.3%, glucose1%, MgSO4?7H2O0.2%, agar2%.3. The growth curve and culture conditions of Saccharopolyspora spinosa, such as culture temperature,culture broth quantity in flask, rotation speed of shaker and the number of glass beads in seed medium were studied. Meanwhile, the Gompertz equation was used to fit and predict the growth curve of Saccharopolyspora spinosa.The results showed that Saccharopolyspora spinosa grew well in the situation of culture temperature29℃, volume of medium30mL/250mL flask, rotation speed240r/min and6glass beads.4. Initial studie to optimize carbon source for the spinosad production was performed, and the optimum fermentation medium for strain N8-30-37was confirmed:glucose6.5%, soluble starch8.5%, cottonseed protein2.8%, peptone2%, NH4NO40.09%, NaCl0.3%, K2HPO40.1%, FeSO40.005%, CaCO30.5%, pH7.2, and the spinosad yield in the optimum fermentation Medium was increased by100%, up to410.25μg/mL.5. Based on the results in shaking flasks’fermentation, spinosad fermentation was scaled up in a100L fermentor, and a productivity of84.36μg/mL was obtained, which was lower than that in the shaking flasks.