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Journal of Bacteriology, September 2009, p. 5471-5479, Vol. 191, No. 17
0021-9193/09/$08.00+0     doi:10.1128/JB.00148-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

OpnS, an Outer Membrane Porin of Xenorhabdus nematophila, Confers a Competitive Advantage for Growth in the Insect Host{triangledown} ,{dagger}

Ransome van der Hoeven and Steven Forst*

Department of Biological Sciences, University of Wisconsin, Milwaukee, Wisconsin 53201

Received 3 February 2009/ Accepted 17 May 2009

The gammaproteobacterium Xenorhabdus nematophila engages in a mutualistic association with an entomopathogenic nematode and also functions as a pathogen toward different insect hosts. We studied the role of the growth-phase-regulated outer membrane protein OpnS in host interactions. OpnS was shown to be a 16-stranded β-barrel porin. opnS was expressed during growth in insect hemolymph and expression was elevated as the cell density increased. When wild-type and opnS deletion strains were coinjected into insects, the wild-type strain was predominantly recovered from the insect cadaver. Similarly, an opnS-complemented strain outcompeted the {Delta}opnS strain. Coinjection of the wild-type and {Delta}opnS strains together with uncolonized nematodes into insects resulted in nematode progeny that were almost exclusively colonized with the wild-type strain. Likewise, nematode progeny recovered after coinjection of a mixture of nematodes carrying either the wild-type or {Delta}opnS strain were colonized by the wild-type strain. In addition, the {Delta}opnS strain displayed a competitive growth defect when grown together with the wild-type strain in insect hemolymph but not in defined culture medium. The {Delta}opnS strain displayed increased sensitivity to antimicrobial compounds, suggesting that deletion of OpnS affected the integrity of the outer membrane. These findings show that the OpnS porin confers a competitive advantage for the growth and/or the survival of X. nematophila in the insect host and provides a new model for studying the biological relevance of differential regulation of porins in a natural host environment.

* Corresponding author. Mailing address: Department of Biological Sciences, P.O. Box 413, University of Wisconsin, Milwaukee, WI 53201. Phone: (414) 229-6373. Fax: (414) 229-3926. E-mail: sforst{at}uwm.edu

{triangledown} Published ahead of print on 22 May 2009.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, September 2009, p. 5471-5479, Vol. 191, No. 17
0021-9193/09/$08.00+0     doi:10.1128/JB.00148-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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