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

Abstract

SummaryLegionella 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.

Nonhematopoietic Cells Are Key Players in Innate Control of Bacterial Airway Infection

“…The L. pneumophila strains used in this study were JR32 (wild type Philadelphia-1) (19), JR32-GFP (20), GS3011 (DT, icmT deletion mutant lacking a functional Icm/Dot T4SS) (21), and DT-GFP (20). L. pneumophila was grown for 3 d on charcoal yeast extract agar plates.…”

The Legionella Autoinducer Synthase LqsA Produces an α-Hydroxyketone Signaling Molecule

“…2) and Vibrio spp., lqsA and lqsS homologues are found in a number of environmental bacteria, including Nitrococcus mobilis, Burkholderia xenovorans, and Polaromonas spp. (29). Accordingly, intercellular signaling involving ␣-hydroxyketones might be common among different bacterial species and genera.…”

“…pneumophila response regulators such as LetA (GacA) (18,25,26), CpxR (27), and PmrA (28) have also been implicated in the regulation of transmissive traits including virulence. Recently, we characterized the putative response regulator LqsR as a novel element of the L. pneumophila virulence regulatory network controlled by RpoS and LetA (29). LqsR promotes pathogen-host cell interactions such as phagocytosis, formation of the Legionella-containing vacuole, intracellular replication and toxicity while inhibiting the entry of L. pneumophila into the replicative growth phase.…”

FliA expression analysis and influence of the regulatory proteins RpoN, FleQ and FliA on virulence and in vivo fitness in Legionella pneumophila

“…Flagellar gene expression is thought to be regulated by this CsrA-dependent pathway. However, RpoS and the response regulator LqsR were also shown to be involved in the expression of the flagellin gene (flaA) (Tiaden et al 2007;Swanson 2001, 2004).…”