Effect of particle aggregation on the survival of irradiated vaccinia virus.

Galasso, G. J. (University of North Carolina School of Medicine, Chapel Hill), and D. G. Sharp. Effect of particle aggregation on the survival of irradiated vaccinia virus. J. Bacteriol. 90:1138-1142. 1965.-The survival curve (plaque titer versus time) of vaccinia virus irradiated with ultraviolet light was found to be strongly dependent, in both shape and general slope, on the degree of aggregation among the virus particles. When special care was taken to produce completely dispersed virus, a straight steep line resulted. Some severely aggregated preparations produced a straight line also, but of much less slope. Thus, the straight line, often taken as evidence of complete dispersion, is not a reliable measure for vaccinia virus. None of the experimental curves resembled the classical multihit curve predicted by the Poisson function for the behavior of uniformly aggregated virus. The aggregation was observed, by electron microscopy, to be nonuniform, and of such a distribution that the survival curves can be qualitatively accounted for in terms of multiplicity reactivation of irradiated virus within cells that receive groups of two or more particles. The greatly increased survival value of aggregates of virus, which indicates multiplicity reactivation, is worthy of note.