Variable virulence phenotype of Xenorhabdus bovienii (γ-Proteobacteria: Enterobacteriaceae) in the absence of their vector hosts
2017
Mcmullen Ii, John G. | Mcquade, Rebecca | Ogier, Jean-Claude | Pages, Sylvie | Gaudriault, Sophie | Stock, Patricia S. | School of Animal and Comparative Biomedical Sciences ; University of Arizona | Postdoctoral Excellence in Research and Teaching (PERT) Fellow, Center for Insect Science ; University of Arizona | Diversité, Génomes & Interactions Microorganismes - Insectes [Montpellier] (DGIMI) ; Institut National de la Recherche Agronomique (INRA)-Université Montpellier 2 - Sciences et Techniques (UM2)-Université de Montpellier (UM) | Department of Entomology ; Michigan State University [East Lansing] ; Michigan State University System-Michigan State University System | National Science Foundation [NSF-IOS-0840932; IOS-0724978]; National Institute of Health grant through BRAVO! (Biomedical Research Abroad: Vistas Open!) [MHIRT 5-T37-MD001427]; University of Arizona Graduate and Professional Student Council Research Program [RSRCH-317FY'15]
Xenorhabdus bovienii bacteria have a dual lifestyle: they are mutualistic symbionts to many species of Steinernema nematodes and are pathogens to a wide array of insects. Previous studies have shown that virulence of X.bovienii-Steinernema spp. pairs decreases when the nematodes associate with non-cognate bacterial strains. However, the virulence of the X. bovienii strains alone has not been fully investigated. In this study, we characterized the virulence of nine X. bovienii strains in Galleria mellonella and Spodoptera littoralis and performed a comparative genomic analysis to correlate observed phenotypes with strain genotypes. Two X. bovienii strains were found to be highly virulent against the tested insect hosts, while three strains displayed attenuated insect virulence. Comparative genomic analyses revealed the presence of several clusters present only in virulent strains, including a predicted type VI secretion system (T6SS). We performed intra-species-competition assays, and showed that the virulent T6SS+ strains generally outcompeted the less virulent T6SS- strains. Thus, we speculate that the T6SS in X. bovienii may be another addition to the arsenal of antibacterial mechanisms expressed by these bacteria in an insect, where it could potentially play three key roles: (1) competition against the insect host microbiota; (2) protection of the insect cadaver from necrotrophic microbial competitors; and (3) outcompeting other Xenorhabdus species and/or strains when co-infections occur.
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