Screening, identification, and biocontrol effect of bacteria against empty-gut disease of Antheraea pernyi

Abstract:

[Objective] To isolate and screen bacteria against Enterococcus pernyi (the pathogen of Antheraea pernyi empty-gut disease) from the oak garden soil of Sericultural Research Institute of Liaoning Province and thus to lay a foundation for the biocontrol of the disease. [Methods] Bacteria were isolated from soil by spread plate technique and the antagonistic strain was screened out with the inhibition zone method. The strain was identified according to morphological features, physiological and biochemical characteristics, and molecular biology. The antagonistic strain was labeled with green fluorescent protein with natural transformation method, and the colonization of the antagonistic strain in oak leaves and gut of A. pernyi was determined. The control of empty-gut disease of A. pernyi was identified by indoor and field experiments. [Results] A total of 87 bacterial strains were isolated from soil. Among them, BF-49 was found to have significant antagonistic activity against E. pernyi. The identification results revealed that BF-49 had the closest genetic relationship with Bacillus velezensis. Therefore, it was identified as B. velezensis and named B. velezensis BF-49. The fluorescence-labeled strain BF-49-GFP could colonize in the gut of A. pernyi for 5 days, and the count of BF-49-GFP reached 1.25×10⁴ CFU/g 20 days after inoculation on the oak leaves. The indoor and field control of empty-gut disease by the 10-fold diluted BF-49 fermentation broth was 78.25% and 74.42%, respectively, which were significantly higher than those of the control agents. [Conclusion] The B. velezensis BF-49 has significant control effect on empty-gut disease of A. pernyi, being a candidate strain for developing the biological control agent against empty-gut disease.