Electron microscopic investigations of rotavirus morphogenesis in cell cultures

The replication of simian rotavirus SA11 in GMK cells and of bovine rotavirus in calf kidney cells was studied by electron microscopy. By 30 min post-inoculation (p.i.) SA11 virus was absorbed to the cell membrane in the absence of trypsin and became engulfed into the cell; clusters of viral particles were internalized also into cytoplasmic vacuoles. At 2 hr p.i., viral particles were seen in lysosomes and 6 hr p.i., the first progeny virus was found in the cisternae of endoplasmic reticulum (ER). Precursor virus particles budded from viroplasm into the cisternae of endoplasmic reticulum, where they became enveloped reaching a diameter of 80-90 nm. There was no difference between SA11 virus and bovine rotavirus. Although the budding of rotavirus particles is essential for acquiring of glycoproteins, the envelopment of capsids was transient. After stripping off the envelope, mature particles were formed 65-70 nm in diameter, consisting of either smooth or rough capsids. The final cytocidal stage of cell infection is described.