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© Carmen Buchrieser, Marie-Christine Prevost
Legionella pneumophila et son flagelle, bactérie responsable de pneumopathie aigue grave. Bactérie de l'environnement , l'émergence récente de cette maladie s'explique par son affinité pour les systèmes modernes d'alimentation en eau comme les tours de refroidissement. Image colorisée.
Publication : Journal of bacteriology

Synergistic contribution of the Legionella pneumophila lqs genes to pathogen-host interactions

Scientific Fields
Diseases
Organisms
Applications
Technique

Published in Journal of bacteriology - 19 Sep 2008

Tiaden A, Spirig T, Carranza P, Brüggemann H, Riedel K, Eberl L, Buchrieser C, Hilbi H

Link to Pubmed [PMID] – 18805977

J. Bacteriol. 2008 Nov;190(22):7532-47

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.