Studies on Mutation Breeding in Producing Strain of Streptomycin avermitilis by the Irradiation of Co~(60)γ Ray

To obtain mutation strain of Streptomyces avermitilis with high total tite and effective component B1a of avermectins,the original strains H20-16 of Streptomyces avermitilis was treated fot mutatiom by using Co60γ ray irradiation combined with methionine or 5-Fluorouracil screening models and the avermectin yield and B1a content were analyzed by HPLC.Though screening,the mutation strains Co39-15 and CF(20)-39-61 were obtained with high total titer,being 173.3% and 76.5% higher than the original strain resp.And the mutation strains Co35-9 and CM35-12 were obtained with high B1a content,being 12.1% and 16.7% higher than the original strain resp.It was concluded that the mutation methods of Co60γ ray irradiation combined with methionine or 5-Fluorouracil screening models were effective for obtaining Bla producing strains with high total titer and effective component.