Abstract

A new strain Streptomyces bingchenggensis BC-X-1, in which one of the impute was disappeared had been screened by N-methyl-N’-nitroso-N-nitroso-guanidine (NTG) mutation. In order to improve the yield of milbemycin by the new strain, response surface methodology was employed to optimize the composition of fermentation medium. The Plackett-Burman design indicated that yeast extract, soybean flour, KH₂PO₄, FeSO₄ and CaCO₃ had significant effects on milbemycin production. The concentrations of these five components were investigated using Box-Behnken design and a polynomial model related to medium components concentration effect on milbemycin yield had been established. Analysis of variance (ANOVA) showed a high coefficient of determination (R²) value of 0.9701, which indicated that good agreement between the experimental and predicted values of milbemycin yield. Student’s T-test of each coefficient showed that all the linear and quadratic terms effect were significant. The optimum concentrations of components: yeast extract, soybean flour, CaCO₃, FeSO₄, KH₂PO₄ were 2.58, 2.58, 0.40, 0.0058 and 0.088%, respectively. The yield of milbemycin reached 1110±98 μg/ml, which was 2.61-fold of the initial yield.

Key words: Milbemycin, Streptomyces bingchenggensis, medium optimization, response surface methodology.