Xenorhabdus nematophila lrhAIs Necessary for Motility, Lipase Activity, Toxin Expression, and Virulence inManduca sextaInsects

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Abstract
The gram-negative insect pathogenXenorhabdus nematophilapossesses potential virulence factors including an assortment of toxins, degradative enzymes, and regulators of these compounds. Here, we describe thelysR-likehomologA(lrhA) gene, a gene required byX. nematophilafor full virulence inManduca sextainsects. In several other gram-negative bacteria, LrhA homologs are transcriptional regulators involved in the expression (typically repression) of virulence factors. Based on phenotypic and genetic evidence, we report thatX. nematophilaLrhA has a positive effect on transcription and expression of certain potential virulence factors, including a toxin subunit-encoding gene,xptD1. Furthermore, anlrhAmutant lacks in vitro lipase activity and has reduced swimming motility compared to its wild-type parent. Quantitative PCR revealed that transcript levels of flagellar genes, a lipase gene, andxptD1were significantly lower in thelrhAmutant than in the wild type. In addition,lrhAitself is positively regulated by the global regulator Lrp. This work establishes a role for LrhA as a vital component of a regulatory hierarchy necessary forX. nematophilapathogenesis and expression of surface-localized and secreted factors. Future research is aimed at identifying and characterizing virulence factors within the LrhA regulon.

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