Complete and coreless forms of reovirus (ECHO 10): Ratio of number of virus particles to infective units in the one-step growth cycle

Abstract

Reovirus (ECHO 10) particles were found to be 75 mμ in diameter and polyhedral in shape. By the negative staining technique, about one-quarter to one-half of the virus population were found to be made up of empty protein coats. These two forms were partially separated by density gradient sedimentation, and infectivity was associated with the complete rather than the coreless particles. One-step growth curves in monkey kidney cells indicated that reovirus is characterized by a prolonged growth cycle and by a tendency to accumulate within cells. The eclipse phase was approximately 6 hours; the increase of infectious virus was then exponential, and completion of the replication required a minimum of 54 hours. Fifty per cent of the total amount of virus produced appeared within approximately 39 hours. The average yield per infected cell was approximately 2500 virus particles which contained 225 plaque-forming units (PFU). Thus the particle: PFU ratio was 11. About 20% of the total virus was found to be extracellular through most of the growth cycle, a result suggesting that the virus was released at a very slow rate. Stability at various temperatures was studied and the half-life at 37°C was found to be about 19 hours.