Screening and Molecular Identification of Bacteria from the Midgut of Larvae Exhibiting Antagonistic Activity against Bacterial Symbionts of Entomopathogenic Nematodes.

Entomopathogenic nematodes (Rhabditida: and ) are a group of organisms capable of infecting larvae of insects living in soil, including representatives of the family . Their insecticidal activity is related to the presence of symbiotic bacteria spp. or spp. in the alimentary tract, which are released into the insect body, leading to its death caused by bacterial toxins and septicemia. Although the antibacterial activities of symbionts of entomopathogenic nematodes have been well described, there is insufficient knowledge of the interactions between these bacteria and microorganisms that naturally inhabit the alimentary tract of insects infested by nematodes. In this study, 900 bacterial strains isolated from midgut samples of larvae were tested for their antagonistic activity against the selected five and species. Cross-streak tests showed significant antibacterial activity of 20 isolates. These bacteria were identified as , , , , sp., , , sp., and sp. Since some representatives of the intestinal microbiota of are able to inhibit the growth of and bacteria in vitro, it can be assumed that this type of bacterial interaction may occur at certain stages of insect infection by or nematodes.