Structural differences between foot-and-mouth disease and poliomyelitis viruses influence their inactivation by aziridines

Abstract

Inactivation of foot-and-mouth disease virus (FMDV) and poliovirus by ethyleneimine (EI) and N-acetylethyleneimine (AEI) has been studied at 25 degrees and at 37 degrees C and in different ionic conditions. FMDV is inactivated rapidly in 100 mM Tris pH 7.6 by each reagent at both temperatures. Poliovirus is also inactivated rapidly in 100 mM Tris by EI at both temperatures and by AEI at 37 degrees C. However, it is inactivated much more slowly by AEI at 25 degrees C; but if the virus is first incubated overnight at 2 degrees C with AEI before transferring to 25 degrees C inactivation then proceeds rapidly. Moreover, the rate of inactivation at 25 degrees C is markedly increased if the virus is suspended in 1 mM Tris. We had interpreted these differences as being due to the greater penetrability of poliovirus (i) in 100 mM Tris at 37 degrees C compared with 25 degrees C and (ii) at lower ionic strength. This interpretation has been confirmed by electron microscopy of FMDV and poliovirus particles stained with phosphotungstic acid. At the elevated temperature, poliovirus had an average diameter of 34+/-0. 21 nm and the stain outlined the nucleic acid core and the individual subunits, whereas at 25 degrees C it averaged 28+/-0.13 nm and the stain did not penetrate the particle. This study also showed that the particle diameter alters with changes in buffer concentration, being 28+/-0.13 nm in 100 mM Tris, 31+/-0.16 nm in 10 mM Tris and 34+/-0.21 nm in 1 mM Tris. The changes in poliovirus are reversible as addition of 1/10 volume of 1 M Tris to the virus in 1 mM Tris resulted in the return of the diameter to 28+/-0.13 nm. FMDV, on the other hand, was less sensitive to osmotic differences as its particle diameter only varied by 7% over the 100-fold change in buffer concentration compared with the 22% change observed for poliovirus.