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Journal of Bacteriology, July 2008, p. 4870-4879, Vol. 190, No. 14
0021-9193/08/$08.00+0     doi:10.1128/JB.00358-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Xenorhabdus nematophila lrhA Is Necessary for Motility, Lipase Activity, Toxin Expression, and Virulence in Manduca sexta Insects

Gregory R. Richards, Erin E. Herbert, Youngjin Park, and Heidi Goodrich-Blair^*

Department of Bacteriology, University of Wisconsin-Madison, Madison Wisconsin

Received 11 March 2008/ Accepted 14 May 2008

The gram-negative insect pathogen Xenorhabdus nematophila possesses potential virulence factors including an assortment of toxins, degradative enzymes, and regulators of these compounds. Here, we describe the lysR-like homolog A (lrhA) gene, a gene required by X. nematophila for full virulence in Manduca sexta insects. 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 that X. nematophila LrhA has a positive effect on transcription and expression of certain potential virulence factors, including a toxin subunit-encoding gene, xptD1. Furthermore, an lrhA mutant 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, and xptD1 were significantly lower in the lrhA mutant than in the wild type. In addition, lrhA itself is positively regulated by the global regulator Lrp. This work establishes a role for LrhA as a vital component of a regulatory hierarchy necessary for X. nematophila pathogenesis and expression of surface-localized and secreted factors. Future research is aimed at identifying and characterizing virulence factors within the LrhA regulon.

Published ahead of print on 23 May 2008.

Present address: Department of Entomology, 413 Biological Science Bldg., University of Georgia, Athens, GA 30602.