Stability of tobacco-mosaic virus, Marmor tabaci H, in solutions diluted beyond the end point of infectivity.

Thornberry, H. H. (University of Illinois, Urbana, Ill.) and B. B. Nagaich. Stability of tobacco-mosaic virus, Marmor tabaci H, in solutions diluted beyond the end point of infectivity. J. Bacteriol. 83:1322-1326. 1962.-Tobacco-mosaic virus (TMV) in crude plant extract and in a partially purified preparation was diluted in distilled water, 0.1 m potassium phosphate buffer, and 0.1 m sodium chloride beyond detectable infectivity by usual assays on 12 primary leaves of Scotia beans, Phaseolus vulgaris L. All assays were made with inoculum containing abrasive at pH 8.5 in 0.1 m phosphate buffer. Infectious virus was recovered from each highly diluted solution (10 liters at pH 7.5 and 4 C for 24 hr) by adsorption at pH 2.5 on Celite particles and desorption at pH 8.5 and 40 C with 100 or 150 ml of 0.1 m phosphate buffer. Thus, TMV is not irreversibly inactivated by such dilutions. To ascertain the infectivity of the virus at high dilutions, TMV in crude plant extracts at three dilutions (10(-6), 10(-7), and 10(-8)) was assayed on bean leaves (12 leaves for 10(-6), 120 leaves for 10(-7), and 1,200 leaves for 10(-8)). Infection was obtained from each diluted inoculum (10(-6), 26 total local lesions; 10(-7), 30; and 10(-8), 22). These data support the conclusions that TMV remains infectious at high dilutions and that the failure to obtain infection beyond the end point of infectivity by usual assays is owing to sparsity of infectious virus rather than to viral inactivation. In addition, they suggest that a single viral particle is capable of infecting a susceptible site.