Screening and compound mutagenesis of a highly pathogenic Beauveria bassiana strain infecting silkworm

Abstract:

[Background] The bioactive substances in batryticated silkworms (Bombyx mori larvae infected by the entomopathogenic fungus Beauveria bassiana) are widely used in medicine, healthcare, and cosmetic industries. At present, most of strains used in the production of batryticated silkworms are the spore powder from naturally dead batryticated silkworms without purification, and there is no fixed application concentration, which make it difficult to ensure the mortality of silkworms. It is an important direction in the research and development for industrial production of batryticated silkworm to improve the pathogenicity of B. bassiana strains and screen out highly pathogenic strains with excellent biological characteristics. [Objective] To screen out highly pathogenic strains by ultraviolet-microwave compound mutagenesis and provide elite strains for the factory production of batryticated silkworms. [Methods] A strain of B. bassiana was isolated with the spore dilution method from naturally infected domestic silkworms in Shanxi province. The strain was then mutagenized by UV-microwave combination, and the spore production and pathogenicity of the strain were compared before and after mutagenesis. [Results] The original strain obtained by isolation was identified as B. bassiana and named B. bassiana Bb1003. Considering the mortality and positive mutation rate, we optimized the mutagenesis conditions as UV (15 W) irradiation for 30 min combined with microwave (800 W, rated microwave frequency of 2 450 MHz) treatment for 60 s. Six mutated strains, including UMCM1, UMCM2, UMCM3, UMCM4, UMCM5, and UMCM6, were obtained after screening. UMCM2 caused an infection rate of 97.64% for silkworm, produced spores 2.48 times those of the original strain, and had significantly higher pathogenic capacity for silkworm than the original strain. [Conclusion] A highly pathogenic strain was produced by ultraviolet-microwave compound mutagenesis, which laid a foundation for the mass production of batryticated silkworms.