Xenorhabdus nematophilus as a Model for Host-Bacterium Interactions: rpoS Is Necessary for Mutualism with Nematodes

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Abstract
Xenorhabdus nematophilus , a gram-negative bacterium, is a mutualist of Steinernema carpocapsae nematodes and a pathogen of larval-stage insects. We use this organism as a model of host-microbe interactions to identify the functions bacteria require for mutualism, pathogenesis, or both. In many gram-negative bacteria, the transcription factor ς S controls regulons that can mediate stress resistance, survival, or host interactions. Therefore, we examined the role of ς S in the ability of X. nematophilus to interact with its hosts. We cloned, sequenced, and disrupted the X. nematophilus rpoS gene that encodes ς S . The X. nematophilus rpoS mutant pathogenized insects as well as its wild-type parent. However, the rpoS mutant could not mutualistically colonize nematode intestines. To our knowledge, this is the first report of a specific allele that affects the ability of X. nematophilus to exist within nematode intestines, an important step in understanding the molecular mechanisms of this association.