Function of the fliK Gene in Pseudomonas plecoglossicida Pathogenicity and Epinephelus coioides’ Immune Response

Pseudomonas plecoglossicida is a gram-negative pathogenic bacterium that causes visceral white spot disease in several marine and aquaculture fish species, resulting high mortality severe financial loss. Based on previous RNA sequencing (RNA-seq), fliK gene expression significantly up-regulated P. during infection, indicating may contribute to its bacterial pathogenicity. To investigate the role of , four specific short hairpin RNAs (shRNAs) were designed synthesized according sequence, with three mutants exhibiting significant decrease . The shRNA-406 mutant maximum silencing efficiency (97.5%) was chosen for further study. Compared wild-type (WT) strain, -RNA interference (RNAi) strain resulted growth, motility, chemotaxis, adhesion, biofilm formation Silencing also 95% increase survival rate, 2-day delay onset death, number spots spleen surface infected orange-spotted groupers ( Epinephelus coioides ). In addition, pathogen load lower spleens E. -RNAi than those WT RNA-seq revealed regulated immune response process. WT-infected group, differentially expressed genes (DEGs) -RNAi-infected group enriched 344 345 KEGG pathways at 3 5 days post infection (dpi), respectively. Among these pathways, 21 system-related enriched, including natural killer (NK) cell-mediated cytotoxicity, platelet activation, Th17 cell differentiation signaling pathways. NK cytotoxicity pathway most which enhance host’s ability remove pathogens reduce inflammation. This study effects pathogenicity identified main involved coioides.