Bacteriophage SP82G inhibition of an intracellular deoxyribonucleic acid inactivation process in Bacillus subtilis

The stability of SP82G bacteriophage deoxyribonucleic acid (DNA) after its uptake by competent Bacillus subtilis was examined by determining the ability of superinfecting phage particles to rescue genetic markers carried by the infective DNA. These experiments show that a DNA inactivation process within the cell is inhibited after infection of the cell by intact phage particles. The inhibition is maximally expressed 6 min after phage infection and is completely prevented by the addition of chloramphenicol at the time of infection. The protective effect of this function extends even to infective DNA which was present in the cell before the addition of intact phage. Continued protein synthesis does not appear to be a requirement for the maintenance of the inhibition. In an analogous situation, if infectious centers resulting from singly infecting phage particles are exposed to chloramphenicol shortly after the time of infection, an exponential decrease in the survival of infectious centers with time held in chloramphenicol is observed. If the addition of chloramphenicol is delayed until 6 min after infection, the infectious centers are resistant to chloramphenicol. The sensitivity of infectious centers treated with chloramphenicol at early times after infection is strongly dependent upon the multiplicity of infection and is consistent with a model of multiplicity reactivation. These results indicate that injected DNA is also susceptible to the intracellular inactivation process and suggest that the inhibition of this system is necessary for the successful establishment of an infectious center.