Transcriptomic Analysis of Largemouth Bass (Micropterus salmoides) Liver and Spleen Responses to Shewanella putrefaciens Infection

Shewanella putrefaciens is a significant bacterial pathogen causing high mortality in farmed largemouth bass (Micropterus salmoides). This study investigated the molecular immune responses in its primary target organs, the liver and spleen, via transcriptomic profiling at 24 h post-infection. We identified 458 significantly differentially expressed genes (DEGs) in the liver and 1405 in the spleen. Gene Ontology enrichment analysis revealed organ-specific immune strategies: the liver response was characterized by type I interferon signaling pathway, whereas the spleen response centered on the regulation of innate immune response. Furthermore, Kyoto Encyclopedia of Genes and Genomes pathway analysis showed that fatty acid metabolism and cytokine-cytokine receptor interaction were significantly enriched in the liver. In contrast, the C-type lectin receptor signaling pathway and cytokine-cytokine receptor interaction were the most prominent in the spleen. Several key DEGs (e.g., stat1a, rsad2, pglyrp5, pglyrp6, acaca, stat2, lepb) associated with immune response, metabolic adaptation, and cellular stress were identified, suggesting a coordinated host mechanism involving pathogen recognition, immunomodulation, and tissue repair. These results provide crucial insights into the immunomodulatory processes in largemouth bass against S. putrefaciens infection.