Electrophoretic Properties of Foot-and-mouth Disease Virus Strains and the Selection of Intra-strain Mutants

Twenty-six strains of foot-and-mouth disease virus have been studied by sucrose gradient zone electrophoresis and a broad range of mobility is evident. It has been established that the electrophoretic mobilities of strains are a unique heritable property of the virion. No covariation is evident with several in vivo and in vitro characteristics of these strains but there is a relationship between mobility and immunological type. This relationship is unconnected with serological specificity and probably reflects the phylogenetic divergence of the seven immunological types of foot-and-mouth disease virus.

Two types of stable electrophoretic mutant have been isolated by serial selection, one of which, however, exhibits phenotypic instability. The other is stable but can be shown to be at a selective disadvantage in competition with the normal virus.

It has not been possible to demonstrate phenotypic mixing in progeny from cells infected with electrophoretically different strains or mutants. The biological implications of this are discussed.