Aspects of the growth of poliovirus as revealed by the photodynamic effects of neutral red and acridine orange

Abstract

Abstract The sensitivity to visible light of poliovirus, grown in the presence of neutral red (NR) or acridine orange, increases with concentration of the dyes. Simple mixing of dye and mature virus, whether it occurs inside or outside the cell, has no effect. At a concentration of NR (4 μg/ml) at which virus and cell growth are little affected in darkness, light sensitivity is found to be acquired at or just before the onset of virus maturation, and no earlier portion of the growth cycle is even transiently light sensitive. The presence of NR is not required much before the onset of maturation in order to render nearly all the virus progeny light sensitive. Provided that virus maturation has not already ceased, irradiation with light of intensity sufficient to inactivate nearly all the mature NR virus in a virus-cell complex nevertheless permits some further maturation to occur. However, the amount of virus formed after light treatment is less than that which would have matured in an equivalent time in unirradiated infected cultures. NR virus rapidly loses its light sensitivity after adsorption to fresh cells. This loss is not due to simple entry of an intact NR virus particle into the cell, as NR virus (produced and retained intracellularly) is fully light sensitive. The rate of loss of light sensitivity after adsorption is similar in presence or absence of NR. This rate is also very similar to the rate of loss of light sensitivity of virus grown in acridine orange, and to the rate of gain of antiserum resistance of the infective center. When light-sensitive virus is used to infect cultures in the absence of NR, the virus progeny is completely light resistant.