REPLICATION AND MORPHOGENESIS OF THE TURBOT AQUAREOVIRUS (TRV) IN CELL-CULTURE

The ultrastructural aspects of the replication cycle of the turbot aqu areovirus (TRV) were studied using CHSE-214 cells. Although this virus in general followed the typical pattern of reovirus replication and m orphogenesis, it presented some important differences. Internalisation of virions into the host cell occurred by direct penetration through the plasma membrane (even at temperatures below 4 degrees C), and this step was independent of trypsin treatment. Two size classes of viral particles were detected in the cytoplasm of infected cells: (i) partic les of 30 nm diameter, probably corresponding to cores, located inside cytoplasmic viroplasms, and (ii) 45 nm diameter particles, located in Vesicles of the endoplasmic reticulum, probably corresponding to sing le-shelled virions. Double-shelled complete viral particles (75-80 nm diameter) were only detected at the exterior of the cell. Cores formed inside the viroplasms were transformed into 45 nm immature virions by budding from viroplasms to cytoplasmic vesicles. The vesicles carried those subviral particles towards the periphery of the cell. Final mat uration occurred by budding of the immature virions through the plasma membrane. During this process, incomplete virions acquired an externa l protein layer, to form the 75 nm double-shelled complete virions rel eased to the exterior. Thus, release of TRV viral progeny was not nece ssarily associated with cell lysis. Replication of TRV was cytoplasmic , and some of the ultrastructural changes caused by the viral replicat ion included development of many dense fibrillar bodies, and cell cyto skeleton alterations. (C) 1998 Published by Elsevier Science B.V.