Screening and Optimizing of Fermentation Conditions of the Effective Avermectin B_(1a) Producing Strains from Streptomyces avermitilis

Aim To obtain the effective avermectin B_ 1a producing strains from Streptomyces avermitilis by screening.Mehtods Effective ways were used to obtain high-performace avermectin producing strains,including the method with ion implantation,the composite mutation method with ultraviolet(UV)-ray and lithium chloride in treating the original strains N-5-9.Then fermentation conditions were optimized to obtain the most suitable fermentation condition of mutation strain A-30-6.Results The mutation strain A-30-6 with the total titer up to 6 988.2μg·ml~ -1 was obtained among high-yield avermectins producing strains and also was proved to be stable effective avermectin B1a producer up to 79.4%.Its proportion of avermectin B1a was 46.3% higher than that of the original strain N-5-9.Conclusion The mutation method with ion implantation and the composite method with ultraviolet(UV)-ray and lithium chloride are effective for to obtaining the goal stains whose total titer and component B1a are distinctly improved by mutations.