Abstract in English, Chinese Pseudomonas plecoglossicida is the pathogen responsible for visceral white spot disease in large yellow croaker (Larimichthys crocea) and orange-spotted grouper (Epinephelus coioides). Previously, RNA sequencing showed that P. plecoglossicida flgK gene expression was significantly up-regulated in orange-spotted grouper spleens during infection. To explore the role of flgK in P. plecoglossicida pathogenicity, RNA interference (RNAi) was performed to silence the P. plecoglossicida flgK gene, and the mutant (flgK-RNAi strain) with the best silencing efficiency (89.40%) was chosen for further study. Results showed that flgK gene silencing significantly attenuated P. plecoglossicida motility, adhesion, and biofilm formation. Compared to those fish infected with the wild-type strain of P. plecoglossicida, orange-spotted grouper infected with the flgK-RNAi strain showed a 55% increase in the survival rate and a one-day delay in time of first death, with fewer pathogens in the spleen and fewer white spots on the spleen surface. RNAi of flgK significantly affected the transcriptome and metabolome of the spleen in infected orange-spotted grouper. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the C-type lectin receptor signaling pathway was the most significantly changed immune-related pathway and the mitogen-activated protein kinase (MAPK) signaling pathway was related to multiple immune-related pathways. Furthermore, arginine biosynthesis and glycerophospholipid metabolism were the most significantly changed metabolism-related pathways. These findings suggest that flgK is a virulence gene of P. plecoglossicida. Furthermore, flgK appears to be involved in the regulation of motility, adhesion, and biofilm formation in P. plecoglossicida, as well as in the regulation of inflammatory and immune responses of orange-spotted grouper to P. plecoglossicida infection. 变形假单胞菌（Pseudomonas plecoglossicida）是引起大黄鱼（Larimichthys crocea）和斜带石斑鱼（Epinephelus coioides）内脏白点病的病原菌。本实验室早期的转录组测序结果发现在整个感染期间，斜带石斑鱼脾脏中变形假单胞菌的flgK基因持续高表达，这说明flgK基因可能与变形假单胞菌的致病性有关。为了研究flgK基因在变形假单胞菌致病性中的具体作用，本文采用RNA干扰技术沉默了变形假单胞菌的flgK基因，并挑选沉默效率最高（89.40%）的突变株（flgK沉默株）进行后续实验。研究结果发现：flgK基因的沉默显著降低了变形假单胞菌的运动性、粘附能力和生物膜的形成能力；与被变形假单胞菌野生株感染的斜带石斑鱼相比，感染同等剂量flgK沉默株的斜带石斑鱼的存活率提升了55%、首例死亡时间延迟了1天、脾脏中病原体的载量较低、脾脏表面白点数量较少。flgK基因的沉默也显著影响了被变形假单胞菌感染的斜带石斑鱼脾脏的转录组和代谢组。KEGG富集分析显示：C-型凝集素受体信号通路是改变最显著的免疫相关通路，丝裂原活化蛋白激酶（MAPK）信号通路与多条免疫相关通路相关联。此外，精氨酸生物合成和甘油磷脂代谢是变化最显著的代谢相关通路。本文研究结果表明：flgK是变形假单胞菌的毒力基因；flgK基因参与了变形假单胞菌的运动性、粘附能力和生物膜形成能力的调控；flgK基因还能影响斜带石斑鱼对变形假单胞菌感染的炎症和免疫应答。.