title: The Legionella pneumophila response regulator LqsR promotes host cell interactions as an element of the virulence regulatory network controlled by RpoS and LetA.
abstract: Legionella pneumophila is an opportunistic human pathogen that replicates within environmental amoebae including Acanthamoeba castellanii and Dictyostelium discoideum. The Icm/Dot type IV secretion system promotes phagocytosis and intracellular replication of L. pneumophila in an endoplasmic reticulum-derived 'Legionella-containing vacuole' (LCV). L. pneumophila adopts a biphasic life cycle consisting of a replicative growth phase and a transmissive (stationary) phase, the latter of which is characterized by the preferential expression of genes required for motility and virulence. A bioinformatic analysis of the L. pneumophila genome revealed a gene cluster homologous to the Vibrio cholerae cqsAS genes, encoding a putative quorum sensing autoinducer synthase (lqsA) and a sensor kinase (lqsS), which flank a novel response regulator (lqsR). We report here that an L. pneumophila lqsR deletion mutant grew in broth with the same rate as wild-type bacteria, but entered the replicative growth phase earlier. Overexpression of lqsR led to an elongated morphology of the bacteria. The lqsR mutant strain was found to be more salt-resistant and impaired for intracellular growth in A. castellanii, D. discoideum and macrophages, formation of the ER-derived LCV and toxicity. Moreover, L. pneumophila lacking LqsR, as well as strains lacking the stationary sigma factor RpoS or the two-component response regulator LetA, were phagocytosed less efficiently by A. castellanii, D. discoideum or macrophages. The expression of lqsR was dependent on RpoS and, to a lesser extent, also on LetA. DNA microarray experiments revealed that lqsR regulates the expression of genes involved in virulence, motility and cell division, consistent with a role for LqsR in the transition from the replicative to the transmissive (virulent) phase. Our findings indicate that LqsR is a novel pleiotropic regulator involved in RpoS- and LetA-controlled interactions of L. pneumophila with phagocytes.
authors.affiliation: Institute of Microbiology, ETH Zürich, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland.
authors.forename: André
authors.initials: A
authors.lastname: Tiaden
authors.forename: Thomas
authors.initials: T
authors.lastname: Spirig
authors.forename: Stefan S
authors.initials: SS
authors.lastname: Weber
authors.forename: Holger
authors.initials: H
authors.lastname: Brüggemann
authors.forename: Rachel
authors.initials: R
authors.lastname: Bosshard
authors.forename: Carmen
authors.initials: C
authors.lastname: Buchrieser
authors.forename: Hubert
authors.initials: H
authors.lastname: Hilbi
mesh_terms: D048248:Acanthamoeba castellanii / Q000382:microbiology; D000818:Animals; D001426:Bacterial Proteins / Q000502:physiology*; D002455:Cell Division / Q000235:genetics; D002460:Cell Line; D004023:Dictyostelium / Q000382:microbiology; D017353:Gene Deletion; D018628:Gene Dosage; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D016952:Legionella pneumophila / Q000166:cytology / Q000235:genetics / Q000254:growth & development*; D008124:Locomotion / Q000235:genetics; D008264:Macrophages / Q000382:microbiology; D020411:Oligonucleotide Array Sequence Analysis; D012808:Sigma Factor / Q000502:physiology*; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D014774:Virulence
chemical_list: D001426:Bacterial Proteins; C068355:CcdA protein, Bacteria; D012808:Sigma Factor; D014157:Transcription Factors; C069567:sigma factor KatF protein, Bacteria