Pathogenicity, ultrastructure and genomics analysis of Nocardia seriolae isolated from largemouth bass (Micropterus salmoides).

Fish granulomatous diseases induced by Nocardia seriolae have caused significant economic losses in global aquaculture. Understanding the structural and genetic basis of N. seriolae' s survival and immune evasion strategies is crucial. However, while some aspects of its pathogenicity have been explored, a comprehensive characterization of its ultrastructural features and the associated genetic determinants, especially in direct correlation, has remained incompletely elucidated. In this study, we utilized specialized staining methods to further characterize the pathology of chronic granulomatous inflammation induced by N. seriolae in largemouth bass (Micropterus salmoides). Using scanning electron microscope (SEM) and transmission electron microscope (TEM), we revealed further insights into the morphological (surface structure, cell wall) and intracellular features (mesosomes, ribosomes, lipids) of N. seriolae, alongside diverse division patterns. Through genomic analysis, the gene clusters related to cell wall synthesis and cell division were characterized, including peptidoglycan, arabinogalactan, mycolic acids (MAs) synthesis, and the division and cell wall (DCW) gene cluster, highlighting the conservation and potential functions of these genes in these processes. In conclusion, these findings provide crucial foundational knowledge regarding the ultrastructure and genetic determinants potentially involved in the pathogenicity of N. seriolae. By integrating detailed ultrastructural observations with genomic insights, this study enhances our understanding of its complex biology and aims to strengthen the foundation for the development of prevention, control, and detection methods for fish granulomatous diseases.