Résumé
Background and Aims: Microorganisms produce a variety of molecules to interact with their host. Xenorhabdus is an entomopathogenic bacterium involved in mutualistic relationship with Steinernema nematodes. Xenorhabdus also produces different specialized metabolites during its complex life cycle: i) pathogenic phase within insect larvae, ii) necrotrophic phase in the insect cadaver, and iii) symbiotic phase with its nematode host. PAXs are a family of Non-Ribosomal Peptides Synthetase (NRPS) cyclolipopeptides produced by almost all Xenorhabdus strains. Besides their antimicrobial activities against Gram-positive bacteria and phytopathogenic fungi, little is known about the ecological role of PAXs in the life cycle of Xenorhabdus, which this work aims to investigate. Methods: The Xenorhabdus nematophila F1 wild-type strain and the ΔpaxA mutant were subjected to antimicrobial susceptibility tests, motility and biofilm assays, pathology assays on insect larvae, and biochemical analyses to assess their phenotypic differences. Aposymbiotic nematodes were used to evaluate PAXs impact in bacterial-host association. Results: Slight differences in insect larval pathogenicity were observed between F1 and ΔpaxA strains. No antimicrobial activity of PAXs peptides on Steinernema carpocapsae and insect microbiota were identified. The involvement of PAXs in motility and biofilm formation was demonstrated in vitro. Reassociation of aposymbiotic nematodes with ΔpaxA mutant resulted in weaker nematode progeny production. Conclusions: Overall, these results suggest that PAXs are not involved in the insect pathogenic phase or in the interaction with the microbiota present in the insect cadaver. Therefore, the involvement of PAXs in the bacterial-nematode host association will be investigated.