Thermal inactivation of tobacco necrosis virus

The thermal inactivation point of different strains of tobacco necrosis virus (TNV) in infective sap ranged between 85° for strain B and 95° for strains D and E. Determination of inactivation points and results of kinetic experiments place the six strains in the same order of susceptibility to heat. TNV did not become inactivated exponentially at the same rate at all survival levels. The virus apparently was inactivated at two different rates, as though it consisted of two components. At high temperatures the more resistant component was a small fraction of the total, but increased with decreasing temperature and at about 40° was the only one detectable. The inactivation rates of the two components differed greatly and increased with increases in temperature. The ratio of the two components and their inactivation rates at different temperatures differed with different strains. The changing ratio of the two components, and some other properties of the strains, show that the virus preparations were initially homogeneous and that the two components were produced by heating. Nucleic acid extracted from strains A and E with phenol became inactivated similarly at 50° to intact virus, indicating that changes in the nucleic acid are responsible for thermal inactivation of the virus. Inactivation to 1% survival in water or acid buffers did not alter the antigenicity, sedimentation coefficient, or the UV absorption spectrum of the virus. Also, there was no evidence that nucleic acid was released under these conditions.