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Appl. Environ. Microbiol. doi:10.1128/AEM.02947-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

New Insights into the Colonization and Release Processes of Xenorhabdus nematophila and the Morphology and Ultrastructure of the Bacterial Receptacle of its Nematode Host, Steinernema carpocapsae

Department of Biological Sciences, University of Wisconsin-Milwaukee; Department of Entomology, University of Arizona. Tucson, AZ 85721-0036.; Universidad de Sonora, Unidad Caborca, Sonora, Mexico

^* To whom correspondence should be addressed. Email: sforst{at}uwm.edu.

	Abstract

We present results from epifluorescence, differential interference contrast and transmission electron microscopy showing that Xenorhabdus nematophila colonizes a receptacle in the anterior intestine of the infective juvenile (IJ) stage of Steinernema carpocapsae. This region is connected to the esophagus at the esophago-intestinal junction. The process by which X. nematophila leave this bacterial receptacle had not been analyzed previously. In this study we monitored the movement of GFP-labeled bacteria during the release process. Our observations revealed that Xenorhabdus colonizes the distal region of the receptacle and that exposure to insect hemolymph stimulated forward movement of the bacteria to the esophago-intestinal junction. Continued exposure to hemolymph caused a narrow passage in the distal receptacle to widen allowing movement of Xenorhabdus down the intestine and out the anus. Efficient release of both the wild type and a non-motile strain was evident in most of the IJs incubated in hemolymph, whereas only a few IJs incubated in nutrient-rich broth released bacterial cells. Incubation of IJs in hemolymph treated with agents that induce nematode paralysis dramatically inhibited the release process. These results suggest bacterial motility is not required for movement out of the distal region of the receptacle and that hemolymph-induced pharyngeal pumping provides a force for the release of X. nematophila out of the receptacle and into the intestinal lumen.

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