Bacteria from the Midgut of Common Cockchafer (<i>Melolontha melolontha</i> L.) Larvae Exhibiting Antagonistic Activity Against Bacterial Symbionts of Entomopathogenic Nematodes: Isolation and Molecular Identification

• Main Authors: Marcin Skowronek, Ewa Sajnaga, Małgorzata Pleszczyńska, Waldemar Kazimierczak, Magdalena Lis, Adrian Wiater
• Format: Article
• Language: English
• Published: MDPI AG 2020-01-01
• Series: International Journal of Molecular Sciences
• Subjects: <i>melolontha melolontha</i>; midgut microbiota; entomopathogenic nematodes; bacterial interactions; <i>xenorhabdus</i>; <i>photorhabdus</i>
• Online Access: https://www.mdpi.com/1422-0067/21/2/580

The mechanisms of action of the complex including entomopathogenic nematodes of the genera <i>Steinernema</i> and <i>Heterorhabditis</i> and their mutualistic partners, i.e., bacteria <i>Xenorhabdus</i> and <i>Photorhabdus</i>, have been well explained, and the nematodes have been commercialized as biological control agents against many soil insect pests. However, little is known regarding the nature of the relationships between these bacteria and the gut microbiota of infected insects. In the present study, 900 bacterial isolates that were obtained from the midgut samples of <i>Melolontha melolontha</i> larvae were screened for their antagonistic activity against the selected species of the genera <i>Xenorhabdus</i> and <i>Photorhabdus</i>. Twelve strains exhibited significant antibacterial activity in the applied tests. They were identified based on 16S rRNA and <i>rpoB</i>, <i>rpoD</i>, or <i>recA</i> gene sequences as <i>Pseudomonas chlororaphis</i>, <i>Citrobacter murliniae</i>, <i>Acinetobacter calcoaceticus</i>, <i>Chryseobacterium lathyri</i>, <i>Chryseobacterium</i> sp., <i>Serratia liquefaciens</i>, and <i>Serratia</i> sp. The culture filtrate of the isolate <i>P. chlororaphis</i> MMC3 L3 04 exerted the strongest inhibitory effect on the tested bacteria. The results of the preliminary study that are presented here, which focused on interactions between the insect gut microbiota and mutualistic bacteria of entomopathogenic nematodes, show that bacteria inhabiting the gut of insects might play a key role in insect resistance to entomopathogenic nematode pressure.