Abstract: 【Aim】 Gut symbiotic bacteria in insects, the main members of the gut microbial community, play important roles in the growth and development, nutrient absorption, and immune system of insects. In this study, a gut symbiotic bacterium of Plutella xylostella was isolated and cultured, and its function was identified to explore the influence of the gut symbiotic bacteria on the adaptability of P. xylostella and the broad-spectrum inhibitory activities against fungi. 【Methods】 The gut bacterium, PxG45, was isolated and purified from the 3rd instar larva of P. xylostella by plate culture in vitro. Morphological characterization, 16S rDNA gene sequencing, and physiological and biochemical characterization were used to identify the bacterial species. The effects of PxG45 on the survival rate of the 3rd instar larva of P. xylostella and the effects of the Beauveria bassiana infection on the survival rate of the 3rd instar larva of P. xylostella were detected by bioassay. The inhibition of PxG45 on B. bassiana was defined by plate confrontation method to further detect the broad-spectrum resistance of PxG45 to the plant pathogenic fungi Colletotrichum higginsianum, C. camelliae, Fusarium oxysporum f. sp. cubense race 4, Alternaria solani, Magnaporthe oryzae and Pseudomonas syringae pv. myricae. 【Results】 PxG45 in the gut of the 3rd instar larva of P. xylostella was identified as Pantoea agglomerans. Compared with the control group which was not fed with PxG45, supplemental PxG45 not only significantly increased the survival rate of the healthy 3rd instar larva of P. xylostella, but also improved the survival rate of the 3rd instar larva infected by B. bassiana. The colonial diameters of B. bassiana and six plant pathogenic fungi in antagonistic culture with PxG45 were significantly smaller than those cultured alone of B. bassiana and six plant pathogenic fungi, and the growth of fungi was inhibited after antagonistic culture with PxG45. 【Conclusion】 PxG45 affects the adaptability of P. xylostella by direct and broad-spectrum antibacterial effects, and can significantly inhibit the growth of plant pathogenic fungi. This study demonstrates that PxG45 possesses the potential as a biocontrol bacterium and provides a new way to use the gut symbionts of pest.
Key words: Plutella xylostella; Pantoea agglomerans PxG45; improved survival rate; antifungal activity