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 Pseudomonas aeruginosa. This network has also been associated with regulating many virulence factors P. aeruginosa 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 nahK leads 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 all P. aeruginosa quorum-sensing (QS) systems, with a large upregulation of the Pseudomonas quinolone 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.