The pleiotropic Legionella transcription factor LvbR links the Lqs and c‐di‐GMP regulatory networks to control biofilm architecture and virulence

Abstract

Summary The causative agent of Legionnaires' disease, Legionella pneumophila, colonizes amoebae and biofilms in the environment. The opportunistic pathogen employs the Lqs (Legionella quorum sensing) system and the signalling molecule LAI‐1 (Legionella autoinducer‐1) to regulate virulence, motility, natural competence and expression of a 133 kb genomic “fitness island”, including a putative novel regulator. Here, we show that the regulator termed LvbR is an LqsS‐regulated transcription factor that binds to the promoter of lpg1056/hnox1 (encoding an inhibitor of the diguanylate cyclase Lpg1057), and thus, regulates proteins involved in c‐di‐GMP metabolism. LvbR determines biofilm architecture, since L. pneumophila lacking lvbR accumulates less sessile biomass and forms homogeneous mat‐like structures, while the parental strain develops more compact bacterial aggregates. Comparative transcriptomics of sessile and planktonic ΔlvbR or ΔlqsR mutant strains revealed concerted (virulence, fitness island, metabolism) and reciprocally (motility) regulated genes in biofilm and broth respectively. Moreover, ΔlvbR is hyper‐competent for DNA uptake, defective for phagocyte infection, outcompeted by the parental strain in amoebae co‐infections and impaired for cell migration inhibition. Taken together, our results indicate that L. pneumophila LvbR is a novel pleiotropic transcription factor, which links the Lqs and c‐di‐GMP regulatory networks to control biofilm architecture and pathogen–host cell interactions.

Quorum sensing modulates the formation of virulent Legionella persisters within infected cells

“…The lack of phenotype for Δ lqsR prompted us to look for an alternative response regulator possibly controlling phenotypic heterogeneity. The transcription factor LvbR is negatively regulated by the sensor kinase LqsS 63 . Deletion of lvbR led to a loss in nongrowers in A. castellanii at 24 h p.i.…”

“…Interestingly, the size of the nongrowing intracellular L. pneumophila subpopulation seems also to be controlled by the recently characterized DNA-binding transcription factor LvbR 63 , rather than the response regulator LqsR 33 . LvbR links the Lqs and c-di-GMP regulatory networks 63 , and the comparative proteomics approach documented in this study revealed that the intracellular nongrowing subpopulation shows a 10-30-fold enrichment in various diguanylate cyclases presumably producing c-di-GMP. Further studies will address the role of the second messenger c-di-GMP in regulating intracellular virulent L. pneumophila persisters.…”

“…timer and lqsA are organized as an operon. To construct a complementation plasmid for the Δ lqsS , Δ lqsT , and Δ lvbR mutant strain, The locus P tac - timer was excised from pNP107 using the restriction enzyme ApaI and XmnI and inserted into pNT31 31 , pAK2 32 , and pAK18 63 leading to the plasmid pNP121, pNP122, and pNP123, respectively.…”

Cyclic di-GMP signaling controlling the free-living lifestyle of alpha-proteobacterial rhizobia

“…Reciprocal interaction between QS and c-di-GMP regulatory circuits are well documented, with a general trend of dominant negative control of QS by c-di-GMP (Hochstrasser et al 2019;Lin Chua et al 2017;Waldron et al 2019;Yang et al 2017). In S. meliloti, elevated levels of c-di-GMP repressed transcription of AHL synthase enzyme sinI and lowered abundance of QS signal AHL molecules in the culture medium (Schäper et al 2016) (Figure 3).…”

The structure of the Legionella response regulator LqsR reveals amino acids critical for phosphorylation and dimerization

“…Intriguingly, the c‐di‐GMP and quorum sensing regulatory networks are linked in L. pneumophila . The sensor kinase LqsS negatively regulates a pleiotropic transcription factor termed LvbR ( Legionella virulence and biofilm regulator), which in turn negatively regulates an inhibitor of the diguanylate cyclase Lpg1057 (Hochstrasser et al, ; Tiaden et al, ). LvbR controls pathogen–host cell interactions, biofilm architecture and natural competence.…”