The histidine kinase NahK regulates pyocyanin production through the PQS system.

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 pathogen . This network has also been associated with regulating many virulence factors secretes 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 of leads to a fourfold increase in PYO production, almost exclusively through upregulation of phenazine operon two (). We determined that this upregulation is due to mis-regulation of all quorum-sensing (QS) systems, with a large upregulation of the quinolone signal system and a decrease in production of the acyl-homoserine lactone-producing system, . 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. IMPORTANCE is a Gram-negative bacterium that establishes biofilms as part of its pathogenicity. infections are associated with nosocomial infections. As the prevalence of multi-drug-resistant increases, it is essential to understand underlying virulence molecular mechanisms. Histidine kinase NahK is one of several kinases in implicated 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 the lifestyle, including regulating bacterial communication mechanisms such as quorum sensing. These effects have larger implications in infection as they affect toxin production and virulence.