Search

The gammaproteobacteriumXenorhabdus nematophilaengages 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.opnSwas expressed during growth in insect hemolymph and expression was elevated as the cell density increased. When wild-type andopnSdeletion strains were coinjected into insects, the wild-type strain was predominantly recovered from the insect cadaver. Similarly, anopnS-complemented strain outcompeted the ΔopnSstrain. Coinjection of the wild-type and ΔopnSstrains 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 ΔopnSstrain were colonized by the wild-type strain. In addition, the ΔopnSstrain displayed a competitive growth defect when grown together with the wild-type strain in insect hemolymph but not in defined culture medium. The ΔopnSstrain 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 ofX. nematophilain the insect host and provides a new model for studying the biological relevance of differential regulation of porins in a natural host environment.