Mutation Breeding of a Streptomycin avermitlis by ~(60)Co γ-ray Irradiation and Study on Radiation Effect

[Objective] The aim was to mutate Streptomyces avermitlis by 60Co γ-ray irradiation so as to screen mutant strain which could improve the yield of B1a.[Method] A Streptomyces avermitlis Av2 without any mutation was mutated by 60Co γ-ray irradiation under 200-1 600 Gy of irradiation-dosage and 10 Gy/min of dose-rate.The relationship among lethality,mutation dispersion,the morphological change of strains and the irradiation dosage of 60Co γ-ray were explored.The primary screening and secondary screening were carried out by inhibition zone method and bottle-shaped fermentation culture,respectively;the content of avermectin was determined by HPLC.[Result] Three mutants of Av2-m212,Av2-m245 and Av2-m286 whose B1a productions were respectively increased by 36%,41% and 46% were obtained under 800 Gy of irradiation-dosage,and they all belonged to shrinkage type.All mutations more than 30% of efficient generated under the condition of 800 Gy-dosage,and the dose was the crossing point of lethality and positive mutation dispersion which tended to be stable.After 60Co γ-ray irradiation,The shrinkage type and volcanic type mutant strains belonged to positive mutation,while the other type mutant strains belonged to negative mutation.[Conclusion] 60Co γ-ray is an effective and promising mutation method for Streptomyces avermitlis and other microorganisms.