Isodensity Ultracentrifugation of Foot-and-Mouth Disease Virus in Caesium Chloride

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Abstract
A rapid centrifugation method for purifying foot-and-mouth disease virus (FMDV) combined an isodensity separation below a moving zone separation in the same tube. Two ml. of crude infectious fluid were introduced over a 3 ml. nonlinear CsCl gradient in a swinging bucket rotor. This preformed gradient provided a gradual increase from density 1.0 to 1.3 g./ml. and a step from 1.3 to 1.6 g./ml. After centrifugation for 4 hr. at 37,000 rev./min. (120,000 g) and 4[degree], a 1 mm. wide light scattering zone was observed with type A virus near the bottom, clearly separated below debris extending from density 1.3 to the meniscus. The narrow light scattering zone contained (40 [plus or minus] 12%) of the FMDV infectivity and its CsCl isodensity was 1.43 [plus or minus] 0.01 g./ml. Southern bean mosaic virus and bacteriophage [PHI] X174 behaved similarly and were useful as density markers. Virus suspensions concentrated an average of 8 fold retained (47 [plus or minus] 16%) of their infectious units and were studied in the analytical ultracentrifuge directly. Dialysed concentrated virus revealed characteristic particles in an electron micro-scope. Exposure to concentrated impure CsCl decreases the stability of the infectivity to such an extent that in 40% CsCl its half-life is about 4 days.