AUTHOR=Shi Lian , Zhao Lingmin , Li Qi , Huang Lixing , Qin Yingxue , Zhuang Zhixia , Wang Xiaoru , Huang Huabin , Zhang Jiaonan , Zhang Jiaolin , Yan Qingpi 

TITLE=Role of the Pseudomonas plecoglossicida fliL gene in immune response of infected hybrid groupers (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂)

JOURNAL=Frontiers in Immunology

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2024.1415744

DOI=10.3389/fimmu.2024.1415744

ISSN=1664-3224

ABSTRACT=<p><italic>Pseudomonas plecoglossicida</italic>, a gram-negative bacterium, is the main pathogen of visceral white-point disease in marine fish, responsible for substantial economic losses in the aquaculture industry. The FliL protein, involved in torque production of the bacterial flagella motor, is essential for the pathogenicity of a variety of bacteria. In the current study, the <italic>fliL</italic> gene deletion strain (Δ<italic>fliL</italic>), <italic>fliL</italic> gene complement strain (C-Δ<italic>fliL</italic>), and wild-type strain (NZBD9) were compared to explore the influence of the <italic>fliL</italic> gene on <italic>P. plecoglossicida</italic> pathogenicity and its role in host immune response. Results showed that <italic>fliL</italic> gene deletion increased the survival rate (50%) and reduced white spot disease progression in the hybrid groupers. Moreover, compared to the NZBD9 strain, the Δ<italic>fliL</italic> strain was consistently associated with lower bacterial loads in the grouper spleen, head kidney, liver, and intestine, coupled with reduced tissue damage. Transcriptomic analysis identified 2 238 differentially expressed genes (DEGs) in the spleens of fish infected with the Δ<italic>fliL</italic> strain compared to the NZBD9 strain. Based on Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, the DEGs were significantly enriched in seven immune system-associated pathways and three signaling molecule and interaction pathways. Upon infection with the Δ<italic>fliL</italic> strain, the toll-like receptor (TLR) signaling pathway was activated in the hybrid groupers, leading to the activation of transcription factors (NF-κB and AP1) and cytokines. The expression levels of proinflammatory cytokine-related genes <italic>IL-1β</italic>, <italic>IL-12B</italic>, and <italic>IL-6</italic> and chemokine-related genes <italic>CXCL9</italic>, <italic>CXCL10</italic>, and <italic>CCL4</italic> were significantly up-regulated. In conclusion, the <italic>fliL</italic> gene markedly influenced the pathogenicity of <italic>P. plecoglossicida</italic> infection in the hybrid groupers. Notably, deletion of <italic>fliL</italic> gene in <italic>P. plecoglossicida</italic> induced a robust immune response in the groupers, promoting defense against and elimination of pathogens via an inflammatory response involving multiple cytokines.</p>