Boon, E. | Search bioRxiv

bioRxiv2024

The Histidine Kinase NahK Regulates Denitrification and Nitric Oxide Accumulation through RsmA inPseudomonas aeruginosa

Pseudomonas aeruginosa have a versatile metabolism; they can adapt to many stressors, including limited oxygen and nutrient availability. This versatility is especially important within a biofilm where multiple microenvironments are present. As a facultative anaerobe, P. aeruginosa can survive under anaerobic conditions utilizing denitrification. This process produces nitric oxide (NO) which has been shown to result in cell elongation. However, the molecular mechanism underlying this phenotype is poorly understood. Our laboratory has previously shown that NosP is a NO-sensitive hemoprotein that works with the histidine kinase NahK to regulate biofilm in P. aeruginosa. In this study, we identify NahK as a novel regulator of denitrification under anaerobic conditions. Under anaerobic conditions, deletion of nahK leads to a reduction of growth coupled with reduced transcriptional expression and activity of the denitrification reductases. Further, during stationary phase under anaerobic conditions, {Delta}nahK does not exhibit cell elongation, which is characteristic of P. aeruginosa. We determine the loss of cell elongation is due to changes in NO accumulation in{Delta} nahK. We further provide evidence that NahK may regulate denitrification through modification of RsmA activity. ImportanceP. aeruginosa is an opportunistic multi-drug resistance pathogen that is associated with hospital acquired infections. P. aeruginosa is highly virulent, in part due to its versatile metabolism and ability to form biofilms. Therefore, better understanding of the molecular mechanisms that regulate these processes should lead to new therapeutics to treat P. aeruginosa infections. The histidine kinase NahK has been previously shown to be involved in both NO signaling and quorum sensing through RsmA. The data presented here demonstrate that NahK is responsive to NO produced during denitrification to regulate cell morphology. Understanding NahKs role in metabolism under anaerobic conditions has larger implications in determining Nahks role in a heterogeneous metabolic environment such as a biofilm.

microbiology↗

bioRxiv2023

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 (P. 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 led to a four-fold 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 systems, with a large upregulation of the Pseudomonas quinolone signal (PQS) 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, this data contributes to understanding how the GacS MKN modulates QS and virulence. ImportancePseudomonas aeruginosa is a Gram-negative bacterium that establishes biofilms as part of its pathogenicity. P. aeruginosa infections are associated with nosocomial infections. As the prevalence of multi-drug resistant P. aeruginosa increases, it is essential to understand underlying virulence molecular mechanisms. Histidine kinase NahK is one of several kinases in P. aeruginosa 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 demonstrates that NahK plays additional important roles in the P. aeruginosa lifestyle, including regulating bacterial communication mechanisms such as quorum sensing. These effects have larger implications in infection as they affect toxin production and virulence.

microbiology↗