Electron Microscopic Observations on the Nature of Vaccinia Virus Particle Aggregation

Abstract

Summary Aggregation among the particles of crude (unpurified) preparations of vaccinia virus is common. Observations with the electron microscope show, in all cases so far examined, that the frequency of groups is greatest for singles and progressively less for each larger size. When the logarithms of group frequency are plotted against the logarithms of group size, the result is a straight line whose slope is a measure of the degree of aggregation. This linear log-log (LLL) distribution is apparent in virus released from cells by freeze-thaw procedure or by ultrasonic waves. It holds for dispersed virus that has been reaggregated by sedimentation into a pellet and resuspended as well as for virus that reaggregates spontaneously. Plaque titrations reveal its influence on the infectivity of aggregated preparations. Its application to interpretation of radiation survival of aggregated virus is discussed. Ultrasonic waves of 20 kc frequency are shown to produce no damage to fresh individual vaccinia virus particles, in intensities necessary for particle dispersion. Freezing at -60°C, heating at 56°C or ultraviolet irradiation (2537 Å) do not predispose the virus to destruction by 20 kc waves.