Screening and fermentation optimization of a highly pathogenic Beauveria bassiana strain infecting silkworm larvae

Abstract:

[Background] Beauveria bassiana, a major entomopathogenic fungus, infects silkworm larvae, producing the white muscardine silkworm Bombyx Batryticatus. The bioactive substances in Bombyx Batryticatus are widely used in medical, healthcare, and cosmetic industries. [Objective] In order to provide high-quality strain resources for the preparation of Bombyx Batryticatus, a highly pathogenic B.bassiana strain was screened from 7 B. bassiana strains from different samples of Bombyx Batryticatus, and the fermentation conditions of this strain were optimized. [Methods] We isolated 7 B. bassiana strains (SDJC-1, SDJC-2, SDJC-3, GXHC-1, SDND-BB, AT-3006 and SQJC-1) from different samples of Bombyx Batryticatus. Based on the results of biological characteristics, protease and chitinase activities, and the lethality in silkworm, a strain with high pathogenicity and excellent traits was screened out. Moreover, the fermentation conditions of this strain were optimized. [Results] The strain SDJC-3 had excellent biological characteristics, high sporulation, and the lethal rate of 75% to silkworm. The Bombyx Batryticatus prepared with SDJC-3 was large and plump and had clear ring of silk gland in the cross-section, exhibiting good quality. The optimum fermentation conditions of SDJC-3 were 27 ℃ of the temperature, 180 r/min of the rotational speed, and 1/5 of the broth volume ratio (250 mL culture flask). [Conclusion] The findings of this study provide a theoretical basis for the use of B.bassiana to prepare and improve the yield and quality of Bombyx Batryticatus.