The contribution of exbB gene to pathogenicity of Pseudomonas plecoglossicida and its interactions with Epinephelus coioides.

To study the roles of the exbB gene in Pseudomonas plecoglossicida during interactions with Epinephelus coioides, five short hairpin RNAs (shRNAs) were designed and synthesized to silence the exbB gene in P. plecoglossicida which resulted in significant reductions in exbB mRNA expression. The mutant with the best silencing efficiency (89.3%) was selected for further study. Silencing exbB in the exbB-RNA interference (RNAi) strain resulted in a 70% increase in the survival rate and a 3-day delay in the onset of infection in E. coioides. Silencing of the exbB gene also resulted in a significant decrease in the number of white spots on the spleen surface and in the spleen pathogen load. The results of dual RNA-seq showed that exbB silencing in P. plecoglossicida also resulted in a significant change in both the pathogen and host transcriptomes in the spleens of infected E. coioides. Comparative transcriptome analysis showed that silencing exbB caused significant changes in multiple signaling molecules and interaction- and immune system-related genes in E. coioides. Gene silencing also resulted in the differential expression of flagellar assembly and the bacterial secretion system in P. plecoglossicida during the infection period, and most of the DEGs were down-regulation. These host-pathogen interactions may make it easier for E. coioides to eliminate the exbB-RNAi strain of P. plecoglossicida, suggesting a significant decrease in the pathogenicity of this strain. These results indicated that exbB was a virulence gene of P. plecoglossicida which contributed a lot in the pathogen-host interactions with E. coioides.