Isolation， identification and optimization of fermentation conditions of pathogenic bacteria from Tenebrio molitor and their inhibitory effects on plant pathogens

【Objective】The purpose of the study was to research the pathogenic bacteria in the diseased and dead larvae of Tenebrio molitor，the inhibitory effect of pathogenic bacteria on plant pathogens and their optimal fermentation conditions，in order to provide scientific basis for effective prevention and control of T. molitor diseases and biological control of agricultural pests and diseases by using pathogenic bacteria.【Method】Using the diseased and dead T. molitor larvae as materials，the pathogenic bacteria were separated by plate coating method and streaking method. The pathogenicity of pathogenic bacteria was determined according to Koch’ s rule. The taxonomic status of pathogenic strains was determined by morphological observation，physiological and biochemical determination and 16S rDNA sequence analysis. The inhibitory effect of pathogenic bacteria on 12 kinds of plant pathogens was determined by plate confrontation method. The fermentation conditions of pathogenic bacteria were optimized by single factor experiment.【Result】Three strains of pathogenic bacteria were isolated from diseased T. molitor，and the strain with the best pathogenic effect was screened and named WU-1， which had a mortality rate of 58.00% against T. molitor larvae. WU-1 strain had broad-spectrum antibacterial activity against 12 plant pathogens tested，and the antibacterial rate was 60.54%-78.33%. Combined with the colony morphological characteristics，physiological and biochemical determination and 16S rDNA sequence analysis results，WU-1 strain was identified as Bacillus velezensis. The optimization results of fermentation conditions of WU-1 strain showed that the optimum medium was YSP medium. The optimum fermentation conditions were a filling volume of 30 mL in 250 mL triangular flask，an initial pH of 8，an inoculation amount of 50 μL，a culture temperature of 40 ℃，a rotation speed of 240 r/min，and a fermentation time of 24 h.【Conclusion】The optimized fermentation scheme can be used for rapid and large-scale culture of WU-1 bacterial suspension. WU-1 strain has a good pathogenic effect on T. molitor larvae，which can provide reference for Coleoptera pest control. This strain has a good inhibitory effect on 12 kinds of plant pathogens， and can be used as a candidate strain to develop biological control agents for plant diseases.