Search for: All records

ABSTRACT Many bacterial histidine kinases work in two-component systems that combine into larger multi-kinase networks. NahK is one of the kinases in the GacS Multi-Kinase Network (MKN), which is the MKN that controls biofilm regulation in the opportunistic pathogenPseudomonas aeruginosa. This network has also been associated with regulating many virulence factorsP. aeruginosasecretes to cause disease. However, the individual role of each kinase is unknown. In this study, we identify NahK as a novel regulator of the phenazine pyocyanin (PYO). Deletion ofnahKleads to a fourfold increase in PYO production, almost exclusively through upregulation of phenazine operon two (phz2). We determined that this upregulation is due to mis-regulation of allP. aeruginosaquorum-sensing (QS) systems, with a large upregulation of thePseudomonasquinolone signal system and a decrease in production of the acyl-homoserine lactone-producing system,las. In addition, we see differences in expression of quorum-sensing inhibitor proteins that align with these changes. Together, these data contribute to understanding how the GacS MKN modulates QS and virulence and suggest a mechanism for cell density-independent regulation of quorum sensing. IMPORTANCEPseudomonas aeruginosais a Gram-negative bacterium that establishes biofilms as part of its pathogenicity.P. aeruginosainfections are associated with nosocomial infections. As the prevalence of multi-drug-resistantP. aeruginosaincreases, it is essential to understand underlying virulence molecular mechanisms. Histidine kinase NahK is one of several kinases inP. aeruginosaimplicated in biofilm formation and dispersal. Previous work has shown that the nitric oxide sensor, NosP, triggers biofilm dispersal by inhibiting NahK. The data presented here demonstrate that NahK plays additional important roles in theP. aeruginosalifestyle, including regulating bacterial communication mechanisms such as quorum sensing. These effects have larger implications in infection as they affect toxin production and virulence. 

ABSTRACT Chemical communication between bacteria and between bacteria and the bacteriophage (phage) viruses that prey on them can shape the outcomes of phage-bacterial encounters. Quorum sensing (QS) is a bacterial cell-to-cell communication process that promotes collective undertaking of group behaviors. QS relies on the production, release, accumulation, and detection of signal molecules called autoinducers. Phages can exploit QS-mediated communication to manipulate their hosts and maximize their own survival. In the opportunistic pathogen Pseudomonas aeruginosa , the LasI/R QS system induces the RhlI/R QS system, and in opposing manners, these two systems control the QS system that relies on the autoinducer called PQS. A P. aeruginosa Δ lasI mutant is impaired in PQS synthesis, leading to accumulation of the precursor molecule HHQ, and HHQ suppresses growth of the P. aeruginosa Δ lasI strain. We show that, in response to a phage infection, the P. aeruginosa Δ lasI mutant reactivates QS, which, in turn, restores pqsH expression, enabling conversion of HHQ into PQS. Moreover, downstream QS target genes encoding virulence factors are induced. Additionally, phage-infected P. aeruginosa Δ lasI cells transiently exhibit superior growth compared to uninfected cells. IMPORTANCE Clinical isolates of P. aeruginosa frequently harbor mutations in particular QS genes. Here, we show that infection by select temperate phages restores QS, a cell-to-cell communication mechanism in a P. aeruginosa QS mutant. Restoration of QS increases expression of genes encoding virulence factors. Thus, phage infection of select P. aeruginosa strains may increase bacterial pathogenicity, underscoring the importance of characterizing phage-host interactions in the context of bacterial mutants that are relevant in clinical settings.