The Legionella pneumophila orphan sensor kinase LqsT regulates competence and pathogen–host interactions as a component of the LAI‐1 circuit

Abstract

Legionella pneumophila is an amoeba-resistant opportunistic pathogen that performs cell-cell communication through the signalling molecule 3-hydroxypentadecane-4-one (LAI-1, Legionella autoinducer-1). The lqs (Legionella quorum sensing) gene cluster encodes the LAI-1 autoinducer synthase LqsA, the cognate sensor kinase LqsS and the response regulator LqsR. Here we show that the Lqs system includes an 'orphan' homologue of LqsS termed LqsT. Compared with wild-type L. pneumophila, strains lacking lqsT or both lqsS and lqsT show increased salt resistance, greatly enhanced natural competence for DNA acquisition and impaired uptake by phagocytes. Sensitive novel single round growth assays and competition experiments using Acanthamoeba castellanii revealed that ΔlqsT and ΔlqsS-ΔlqsT, as well as ΔlqsA and other lqs mutant strains are impaired for intracellular growth and cannot compete against wild-type bacteria upon co-infection. In contrast to the ΔlqsS strain, ΔlqsT does not produce extracellular filaments. The phenotypes of the ΔlqsS-ΔlqsT strain are partially complemented by either lqsT or lqsS, but are not reversed by overexpression of lqsA, suggesting that LqsT and LqsS are the sole LAI-1-responsive sensor kinases in L. pneumophila. In agreement with the different phenotypes of the ΔlqsT and ΔlqsS strains, lqsT and lqsS are differentially expressed in the post-exponential growth phase, and transcriptome studies indicated that 90% of the genes, which are downregulated in absence of lqsT, are upregulated in absence of lqsS. Reciprocally regulated genes encode components of a 133 kb genomic 'fitness island' or translocated effector proteins implicated in virulence. Together, these results reveal a unique organization of the L. pneumophila Lqs system comprising two partially antagonistic LAI-1-responsive sensor kinases, LqsT and LqsS, which regulate distinct pools of genes implicated in pathogen-host cell interactions, competence, expression of a genomic island or production of extracellular filaments.

Silencing of natural transformation by an RNA chaperone and a multitarget small RNA

“…4 A and B). The observed reduced transformability in the stationary phase is consistent with a previous report that quorum sensing by the Lqs (Legionella quorum sensing) system represses competence in the stationary phase (29). In contrast to the wild-type strain, both the lpp0148 TAA and ΔrocR strains appear highly transformable in all growth phases (Fig.…”

Life Stage-specific Proteomes of Legionella pneumophila Reveal a Highly Differential Abundance of Virulence-associated Dot/Icm effectors

“…However, its exclusiveness to UNC contradicts the transcriptomic findings of others (155), showing that expression of PilA is affected by sensor kinase LqsS and its homolog LqsT in the stationary phase and that the protein was identified in purified Legionella-containing vacuoles (29). Lpg2958 carries a conserved Clp_protease_NfeD_1 domain (2.31e-94), a domain family which include membrane-bound ClpP class serine proteases acting in protein quality control (156).…”

A Type IV Translocated Legionella Cysteine Phytase Counteracts Intracellular Growth Restriction by Phytate

“…Competitive growth in A. castellanii between wild type and lppA deletion strains was performed as described (47). Finally, the observation of PtdIns(4)P in D. discoideum by GFP-SidC P4C was carried out as described previously (21).…”

“…To this end, the infected cells were lysed after microscopic imaging at a given time point, and bacterial dilutions were plated onto charcoal yeast extract agar following the method described previously for colony counting (47). D. discoideum amoebae were lysed and plated without imaging.…”