Effect of the zinc transporter ZupT on the virulence mechanisms of mesophilic Aeromonas salmonicida SRW-OG1

As a typical psychrophilic bacterial pathogen, Aeromonas salmonicida causes furunculosis in wild and farmed freshwater and marine fish, leading to substantial economic losses in the global aquaculture industry. Previous studies have shown that A. salmonicida is unable to grow above 25°C, hence limiting its infection to cold-water fish. However, we isolated A. salmonicida SRW-OG1, a mesophilic pathogenic strain from the warm-water fish Epinephelus coioides. Through RNA-seq analysis, we observe significant upregulation of the zupT gene at 28°C. ZupT is a member of zinc-regulated transporters and iron-regulated transporter-like proteins (ZIP family) and is closely associated with transcriptional regulation of virulence in certain pathogens. Consequently, our study aimed to examine the role of zupT during A. salmonicida SRW-OG1 infection at high temperatures. Our findings demonstrate that the zupT-RNAi strain exhibits severe growth restriction under limited Zn²⁺ and Fe²⁺ conditions. Notably, this strain shows significantly reduced mortality rates and colonization abilities. Moreover, its motility, biofilm formation, adhesion, and hemolytic activities are significantly diminished. Confocal laser scanning microscopy reveals earlier and accelerated biofilm dissociation in the zupT-RNAi strain. Analysis of extracellular products at 36 h indicates a considerable reduction in relative extracellular protein content in the zupT-RNAi strain. Taken together, our results highlight the vital role of the zupT gene in zinc transport and the fitness of A. salmonicida SRW-OG1 within the host.