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Journal of Bacteriology, November 2008, p. 7532-7547, Vol. 190, No. 22
0021-9193/08/$08.00+0     doi:10.1128/JB.01002-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Synergistic Contribution of the Legionella pneumophila lqs Genes to Pathogen-Host Interactions{triangledown} ,{dagger}

André Tiaden,1 Thomas Spirig,1 Paula Carranza,2 Holger Brüggemann,3,{ddagger} Kathrin Riedel,2 Leo Eberl,2 Carmen Buchrieser,3 and Hubert Hilbi1*

Institute of Microbiology, ETH Zürich, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland,1 Institute of Plant Biology, University of Zürich, Zollikerstr. 10, 8008 Zürich, Switzerland,2 Unité de Biologie des Bactéries Intracellulaires and CNRS URA 2171, Institut Pasteur, 28 Rue du Dr Roux, 75724 Paris, France3

Received 20 July 2008/ Accepted 9 September 2008

The causative agent of Legionnaires' disease, Legionella pneumophila, is a natural parasite of environmental protozoa and employs a biphasic life style to switch between a replicative and a transmissive (virulent) phase. L. pneumophila harbors the lqs (Legionella quorum sensing) cluster, which includes genes encoding the autoinducer synthase LqsA, the sensor kinase LqsS, the response regulator LqsR, and a homologue of HdeD, which is involved in acid resistance in Escherichia coli. LqsR promotes host-cell interactions as an element of the stationary-phase virulence regulatory network. Here, we characterize L. pneumophila mutant strains lacking all four genes of the lqs cluster or only the hdeD gene. While an hdeD mutant strain did not have overt physiological or virulence phenotypes, an lqs mutant showed an aberrant morphology in stationary growth phase and was defective for intracellular growth, efficient phagocytosis, and cytotoxicity against host cells. Cytotoxicity was restored upon reintroduction of the lqs genes into the chromosome of an lqs mutant strain. The deletion of the lqs cluster caused more-severe phenotypes than deletion of only lqsR, suggesting a synergistic effect of the other lqs genes. A transcriptome analysis indicated that in the stationary phase more than 380 genes were differentially regulated in the lqs mutant and wild-type L. pneumophila. Genes involved in protein production, metabolism, and bioenergetics were upregulated in the lqs mutant, whereas genes encoding virulence factors, such as effectors secreted by the Icm/Dot type IV secretion system, were downregulated. A proteome analysis revealed that a set of Icm/Dot substrates is not produced in the absence of the lqs gene cluster, which confirms the findings from DNA microarray assays and mirrors the virulence phenotype of the lqs mutant strain.

* Corresponding author. Mailing address: Institute of Microbiology, ETH Zürich, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland. Phone: (41) 44 632 4782. Fax: (41) 44 632 1137. E-mail: hilbi{at}micro.biol.ethz.ch

{triangledown} Published ahead of print on 19 September 2008.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

{ddagger} Present address: Max Planck Institute for Infection Biology, Department of Molecular Biology, Charitéplatz 1, 10117 Berlin, Germany.

Journal of Bacteriology, November 2008, p. 7532-7547, Vol. 190, No. 22
0021-9193/08/$08.00+0     doi:10.1128/JB.01002-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



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