The autoinducer synthase LqsA and putative sensor kinase LqsS regulate phagocyte interactions, extracellular filaments and a genomic island of Legionella pneumophila

Abstract

The amoebae-resistant opportunistic pathogen Legionella pneumophila employs a biphasic life cycle to replicate in host cells and spread to new niches. Upon entering the stationary growth phase, the bacteria switch to a transmissive (virulent) state, which involves a complex regulatory network including the lqs gene cluster (lqsA-lqsR-hdeD-lqsS). LqsR is a putative response regulator that promotes host-pathogen interactions and represses replication. The autoinducer synthase LqsA catalyses the production of the diffusible signalling molecule 3-hydroxypentadecan-4-one (LAI-1) that is presumably recognized by the sensor kinase LqsS. Here, we analysed L. pneumophila strains lacking lqsA or lqsS. Compared with wild-type L. pneumophila, the DeltalqsS strain was more salt-resistant and impaired for the Icm/Dot type IV secretion system-dependent uptake by phagocytes. Legionella pneumophila strains lacking lqsS, lqsR or the alternative sigma factor rpoS sedimented more slowly and produced extracellular filaments. Deletion of lqsA moderately reduced the uptake of L. pneumophila by phagocytes, and the defect was complemented by expressing lqsA in trans. Unexpectedly, the overexpression of lqsA also restored the virulence defect and reduced filament production of L. pneumophila mutant strains lacking lqsS or lqsR, but not the phenotypes of strains lacking rpoS or icmT. These results suggest that LqsA products also signal through sensors not encoded by the lqs gene cluster. A transcriptome analysis of the DeltalqsA and DeltalqsS mutant strains revealed that under the conditions tested, lqsA regulated only few genes, whereas lqsS upregulated the expression of 93 genes at least twofold. These include 52 genes clustered in a 133 kb high plasticity genomic island, which is flanked by putative DNA-mobilizing genes and encodes multiple metal ion efflux pumps. Upon overexpression of lqsA, a cluster of 19 genes in the genomic island was also upregulated, suggesting that LqsA and LqsS participate in the same regulatory circuit.

Enterohemorrhagic Escherichia coli Virulence Regulation by Two Bacterial Adrenergic Kinases, QseC and QseE

“…The plant pathogen Agrobacterium tumefaciens uses the kinase ChvG to regulate tumorigenesis by directly or indirectly sensing extracellular acidity (39). Other examples include cis-2-dodecenoic acid sensing by Burkholderia cenocepacia BCAM0227 (43) and LAI-1 sensing by Legionella pneumophila LqsS (75).…”

Essential Role for the Response Regulator PmrA in Coxiella burnetii Type 4B Secretion and Colonization of Mammalian Host Cells

“…LqsRS is a quorum-sensing TCS that indirectly regulates expression of 12 effector-encoding genes (29,34). The sensor kinase LqsS is stimulated by the autoinducer molecule LAI-1, resulting in activation of the response regulator LqsR (35). However, LqsR lacks a DNA-binding motif; consequently, the precise mechanism of gene regulation is unresolved (34).…”

The Legionella pneumophila Collagen-Like Protein Mediates Sedimentation, Autoaggregation, and Pathogen-Phagocyte Interactions

“…To determine if differences in infection between conditions were due to sedimentation or initial binding, infections were also performed with a cen- trifugation at 880 ϫ g for 10 min before the 2-h infection. Afterwards, L. pneumophila internalization was measured by flow cytometry as previously described (18,19) with the addition of a 1-h 100-g/ml gentamicin treatment to kill extracellular bacteria. All L. pneumophila strains used contained a plasmid expressing green fluorescent protein (GFP) under control of a constitutive promoter, and internalization was defined as the acquisition of fluorescence by A. castellanii compared to the uninfected control.…”

“…Sedimentation assays were performed as previously described with few modifications (18,19). L. pneumophila strains were grown for 3 days, and colonies were suspended to an optical density at 600 nm (OD 600 ) of 1 in deionized water with 10% BYE or in deionized water with the addition of the indicated salts.…”