AroC as a key virulence factor and live-attenuated vaccine target in Pseudomonas plecoglossicida

Pseudomonas plecoglossicida is a major etiological agent of visceral white-spot disease in diverse aquaculture species. Chorismate synthase (AroC), a key enzyme in the aromatic amino acid biosynthetic pathway, is essential for central metabolism and has been implicated in bacterial virulence. In this study, an aroC deletion mutant (ΔaroC) and a complemented strain (CΔaroC) were constructed to investigate the role of AroC in virulence regulation and to evaluate its potential as a live-attenuated vaccine candidate. Compared with the wild-type (WT) strain, ΔaroC exhibited significantly reduced growth, motility, hemolytic activity, and biofilm formation. In infection experiments, ΔaroC showed markedly attenuated virulence, resulting in 90% host survival. In a goldfish vaccination-challenge model, immunization with ΔaroC conferred moderate protective efficacy, with a relative percent survival (RPS) of 62%. Transcriptomic analysis revealed that aroC deletion led to the downregulation of genes involved in amino acid metabolism, ABC transporters, and quorum sensing pathways. These results suggest that AroC contributes to pathogenicity by coordinating metabolic processes and environmental adaptation. Together, our findings identify AroC as an important virulence determinant in P. plecoglossicida and suggest that ΔaroC is a promising live-attenuated vaccine candidate that warrants further validation in the natural host.