PvgAS: A novel two-component system that controls type III and type VI secretion systems and virulence in the fish pathogen Pseudomonas plecoglossicida

Pseudomonas plecoglossicida is a Gram-negative bacterium that causes chronic granulomatous diseases in fish. However, the molecular mechanisms underlying its pathogenicity are poorly understood. Here, we identified a novel two-component system (TCS) in P. plecoglossicida, named PvgAS, that regulates the expression of 76 genes, including the type VI secretion system-1 (T6SS-1), a key virulence factor, and the type III secretion system (T3SS) gene cluster. We showed that PvgAS is essential for bacterial virulence in large yellow croaker (LYC), an important aquaculture species, by controlling T6SS-1 expression, which is crucial for tissue colonization and intracellular survival. In contrast, T3SS was dispensable for P. plecoglossicida virulence in this model. We also confirmed T6SS-1 gene regulation by PvgAS at the transcriptional and translational levels using RNA-seq, RT-qPCR, lacZ reporter, and western blot assays. Our study reveals a regulatory and functional role of PvgAS in P. plecoglossicida pathogenicity and suggests that PvgAS may be a potential target for new therapeutic interventions against this bacterium.