HOST CONTROLLED VARIATION IN BACTERIAL VIRUSES

Abstract

Two analogous host-virus systems are described: (a) phage lambda, and its hosts, strains KI2S and C of Escherichia coli, and (b) phage P2, and its hosts, strain B of E. coli and strain Sh of Shigella dysenteriae. In both cases, the phage when passed through one of its host strains (lambda grown on K12S and P2 grown on B) can attack both of its host strains with equal efficiencies, whereas the phage passed through the 2d of its host strains (lambda grown on C and P2 grown on Sh) is extremely inefficient in attacking the first host strain (K12S and B, respectively). The few (of the order of 1 in 10,000 particles of such phage prepns. that succeed in growing on the first host strain, readapt immediately to it. Such changes in infectivity of the phages occur in one growth cycle and do not involve mutation and selection. They occur both in the lytic and in the lysogenic cycles of phage multiplication. The interpretation proposed assumes the existence of a phage structure, the specificity of which is completely or almost completely under control of the host cell, and which is required for some step in the process of phage multiplication.