Host-dependent induction of phage mutants and lysogenization

Abstract

Temperate phage P2 froms plaques with equal efficiency on its hosts Escherichia coli strain C and Shigella dysenteriae strain Sh. When the host was irradiated with ultraviolet light (UV), strain C was found to have a greater capacity than strain Sh to give rise to plaques after infection with either unirradiated or irradiated phage P2. When strain C, irradiated with relatively small doses of UV, was infected with UV-irradiated phage P2, the survival of the phage was greatly increased, compared to that obtained on either unirradiated strain C or Sh, or similarly irradiated strain Sh. Concomitantly, an increased proportion of clear plaque-type mutants was found among the survivors. Ninety-eight such mutants were classified according to their ability to establish lysogeny in either strain Sh or C, and to cooperate with each other in mixed infection to increase the frequency of establishment of lysogeny. Three classes were obtained, the members of one of which had two unusual characteristics: they were able to establish lysogeny in strain C, but not in strain Sh; they gave rise, both spontaneously and after UV treatment, to variants able to establish lysogeny in both strains. A hybrid of strains Sh and C, which was able to be lysogenized by the above class of mutants, retained the same capacity for phage P2 as strain Sh, indicating that these two differences between the strains are independent of each other.