Effects of midgut bacteria inHyphantria cunea(Lepidoptera: Erebidae) on nuclear polyhedrosis virus andBacillus thuringiensis(Bacillales: Bacillaceae)

Abstract

Hyphantria cunea Drury (Lepidoptera: Erebidae) is a quarantine pest in China that can cause damage to hundreds of plants. As biological control agents, Nuclear Polyhedrosis Virus (NPV) and Bacillus thuringiensis Berliner (Bacillales: Bacillaceae) (Bt) are commonly used to inhibit the prevalence of H. cunea. To investigate the role of midgut bacteria in the infection of NPV and Bt in H. cunea, we performed a series of tests, including isolating the dominant culturable bacteria in the midgut, eliminating intestinal bacteria, and respectively inoculating the dominant strains with NPV and Bt for bioassay. Two dominant bacteria, Klebsiella oxytoca Lautrop (Enterobacterales: Enterobacteriaceae) and Enterococcus mundtii Collins (Lactobacillales: Enterococcaceae), in the midgut of H. cunea were identified, and a strain of H. cunea larvae without intestinal bacteria was successfully established. In the bioassays of entomopathogen infection, K. oxytoca showed significant synergistic effects with both NPV and Bt on the death of H. cunea. In contrast, E. mundtii played antagonistic effects. This phenomenon may be attributed to the differences in the physico-chemical properties of the two gut bacteria and the alkaline environment required for NPV and Bt to infect the host. It is worth noting that the enhanced insecticidal activity of K. oxytoca on NPV and Bt provides a reference for future biological control of H. cunea by intestinal bacteria.

The immunostimulatory role of an Enterococcus-dominated gut microbiota in host protection against bacterial and fungal pathogens in Galleria mellonella larvae

“…We were driven to assess if the E. mundtii isolated from the conventional larva gut exhibited inhibition to Btg , as E. mundtii is known to secrete bacteriocins that have previously been shown to have broad-spectrum antimicrobial activity against Gram-negative and Gram-positive bacteria, including Bacillus thuringiensis ( 17 , 43 ). Grau et al.…”

“…Furthermore, a recent study on Hyphantria cunea (Lepidoptera: Erebidae) found that germ-free larvae inoculated with E. mundtii reduced the mortality of larvae infected with Btg as well as a nucleopolyhedrovirus (NPV). However, germ-free larvae inoculated with Klebsiella oxytoca (a species of Gram-negative Enterobacter ) were found to be significantly synergistic with the effects of both Btg and the NPV, resulting in increased mortality ( 17 ). Using the same zone of inhibition technique as Grau et al.…”

“…We were driven to assess if the E. mundtii isolated from the conventional larva gut exhibited inhibition to Btg, as E. mundtii is known to secrete bacteriocins that have previously been shown to have broad-spectrum antimicrobial activity against Gram-negative and Gram-positive bacteria, including Bacillus thuringiensis (17,43). Grau et al (43) found that when Tribolium castaneum (Coleoptera: Tenebrionidae) beetle larvae were inoculated with a A B FIGURE 7 The phenoloxidase (PO) activity in the hemolymph of surviving axenic and conventional larvae infected either (A) orally by Btg, or (B) topically by Mr.…”

“…In some cases, the microbiota may actually facilitate pathogen infections, particularly when there are disruptions to the community caused by dysbiosis. This can result in an elevated risk of septicemia when bacteria breach the gut barrier and enter the hemocoel ( 16 , 17 ). Although the role of the gut microbiota in enhancing host resistance to infections is increasingly studied, the current knowledge of its role and contribution to host tolerance by different pathogens is still limited and fragmented.…”