Genetic Analysis of tox + and tox - Bacteriophages of Corynebacterium diphtheriael RANDALL

mune phages the c markers of phages j3 and y failed to segregate from the imm markers which determine the specificity of lysogenic immunity in these phages. The factor which directs the synthesis of diphtherial toxin during infection of appropriate corynebacterial hosts by toxinogenic corynebacteriophages is designated tox+. It was possible to show that the tox+ determinant of phage ,B behaves as a single genetic element which occupies a position between the loci h and imm on the genetic map of this phage. Genetic recombination between mutants of phage occurred at very low frequencies in biparental matings performed by mixed infection of Corynebacterium diphtheriae C71( _)tox-. Considerably higher recombination frequencies were observed when lysogenic bacterial strains carrying one parental phage as prophage were induced by ultraviolet irradiation and then superinfected by the second parental phage. Maximal stimulation of genetic recombination between mutant #3 phages was detected when superinfection followed ultraviolet irradiation of the lysogenic cells within a limited period of time. In matings between phages with incomplete genetic homology, the stimulation of recombination by ultraviolet radiation was much less effective.