Electron microscopic observations of a marine fish iridovirus isolated from brown-spotted grouper, Epinephelus tauvina

The morphogenesis and the ultrastructure of a marine fish iridovirus isolat ed from diseased grouper, Epinephelus tauvina were studied by electron micr oscopy. The virus was grown on a marine fish cell line (GP) at 25 degreesC. After appearance of advanced cytopathic effect (CPE), various morphogeneti c stages of virus amplification, maturation and assembly were detected in t he cytoplasm of virus-infected cells. The matured nucleocapsids were probab ly formed by insertion of electron-dense core material into a partly formin g empty capsid just before completely sealed. The nucleocapsids were locate d at the assembly sites as pseudocrystalline arrays or scattered individual ly. In the late phase of infection, the nucleocapsids were enveloped and re leased by budding from the plasma membrane. The budding virus particles cou ld directly enter neighbouring cells by endocytosis to start the next round infection. Ultrastructure of the grouper iridovirus was studied using the methods of enzymatic digestions and detergent degradations. The purified ir idovirus particles showed a three-layered membrane including an external li poprotein envelope, an inner periodic protein capsid and a lipid-containing membrane. The regular array of surface capsid subunits was observed after degradation with detergent. (C) 2001 Elsevier Science B.V. All rights reser ved.