The Legionella pneumophila response regulator LqsR promotes host cell interactions as an element of the virulence regulatory network controlled by RpoS and LetA

Cell Microbiol. 2007 Dec;9(12):2903-20. doi: 10.1111/j.1462-5822.2007.01005.x. Epub 2007 Jul 5.


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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acanthamoeba castellanii / microbiology
  • Animals
  • Bacterial Proteins / physiology*
  • Cell Division / genetics
  • Cell Line
  • Dictyostelium / microbiology
  • Gene Deletion
  • Gene Dosage
  • Gene Expression Profiling
  • Gene Expression Regulation, Bacterial
  • Humans
  • Legionella pneumophila / cytology
  • Legionella pneumophila / genetics
  • Legionella pneumophila / growth & development*
  • Locomotion / genetics
  • Macrophages / microbiology
  • Oligonucleotide Array Sequence Analysis
  • Sigma Factor / physiology*
  • Transcription Factors / genetics
  • Transcription Factors / physiology*
  • Virulence


  • Bacterial Proteins
  • CcdA protein, Bacteria
  • Sigma Factor
  • Transcription Factors
  • sigma factor KatF protein, Bacteria