Screening, identification and optimization of fermentation conditions of antagonistic Xenorhabdus bovienii 445 against Aspergillus niger

【Objective】 Entomopathogenic nematode symbiosis have broad antimicrobial spectrum and effective antibacterial effects, so screening strains with highly antagonistic effects against Aspergillus niger from the existing commensal bacteria resources will provide more choices for seeking safe and efficient biopreservation materials. 【Methods】 The existing entomopathogenic nematode symbiosis were preliminarily screened and re screened by plate confrontation method and agar diffusion method respectively, so as to screen the highly antagonistic symbiotic bacteria, identify the highly antagonistic symbiotic bacteria by physiological and biochemical analysis and 16S rRNA sequence evolution analysis, and optimize the strain culture conditions by single factor test and response surface analysis. The control efficiency for Aspergillus niger in Red Globe grape was verified by injury inoculation method. 【Results】 A total of 20 antagonistic symbiotic bacteria were obtained through preliminary isolation and screening, and a symbiotic bacterium (445) with significant antibacterial effect was obtained through re screening. Through physiological, biochemical and molecular biological analysis, it was identified as pathogenic bacterium Xenorhabdus bovienii, Genebank ID: OK560680 through physiological, biochemical and molecular biological analysis. It was clustered in the same branch as strain Xenorhabdus bovienii strain Xb139 (MG995576.1), with a similarity of 99.79%. Through single factor test and response surface analysis, the optimal culture conditions for the antibacterial activity of strain 445 were as follows: inoculation amount of 3.06 %, pH 7.0, liquid volume of 100.15 mL / 250 mL. Under these conditions, the diameter of antibacterial circle was 29.67±0.28 mm, and the antibacterial titer was 10.59 cm/mL, which was 39.16% higher than that before optimization. In the normal temperature antiefficiency experiment of grapes, the fermentation broth of Xenorhabdus bovienii 445 had a better control effect on Aspergillus niger, and the control effect was 63.50 % after 3 days. 【Conclusion】 In this study, entomopathogenic nematode symbiotic bacteria were used to control Aspergillus niger infection during grape storage for the first time, and a highly effective entomopathogenic nematode symbiotic bacteria against Aspergillus niger was screened. Its fermentation broth has good inhibitory effect on Aspergillus niger and good biocontrol potential, which provides new biocontrol materials and research ideas for biocontrol of postharvest pathogen Aspergillus niger.