Pseudomonas aeruginosa uses kinases NahK and RetS to control the motile-biofilm switch

The multidrug-resistant bacterium Pseudomonas aeruginosa ( Pa) poses a significant threat to public health. This Gram-negative bacterium establishes pathogenicity through formation of multicellular communities, known as biofilms, that result in significant resistance to antibiotics and host immune systems. In Pa , the motile-to-biofilm transition is regulated through an interconnected signaling network known as the Gac Multikinase Network (Gac-MKN). This network comprises two regulatory branches: the HptB signaling network and GacS/A signaling network. In the Gac-MKN, several histidine kinases converge to regulate the activity of the post-transcriptional regulator protein, RsmA. Although previous studies have assessed the role of individual kinases in this network, the role of each Gac-MKN kinase in regulating RsmA activity has not been quantitatively characterized and compared in side-by-side experiments in the same reference strain, which is presented here. In this study, we show that kinases NahK and RetS are the predominant regulators of the Gac-MKN. Through controlled testing of RsmA-dependent phenotypes, we demonstrate loss of nahK or retS leads to complete inactivation of RsmA, triggering biofilm formation. Our results support previous findings that RetS regulates RsmA through the GacS/A network but present the new finding that NahK is the central kinase involved in HptB phosphorylation; previous studies have attributed HptB phosphorylation to PA1611 and SagS. Our findings demonstrate that NahK signaling controls RsmA activity to rapidly transition between the motile and biofilm states. We anticipate the results of this study will facilitate the use of targeting the Gac-MKN to trigger biofilm dispersal for improved antibiotic treatment.