The multiplication of vegetative T2 bacteriophage in B/r bacteria has been followed by studying the lethal effects of decay of incorporated radiophosphorus P32 at various stages of the eclipse period.Experiment I. Non-radioactive B/r bacteria were infected with highly radioactive ( i.e . P32-unstable) T2 and infection allowed to proceed at 37°C. for various numbers of minutes before freezing the infected cells and storing them in liquid nitrogen. The longer development had been allowed to proceed at 37°C. before freezing, the slower the inactivation of the frozen infective centers by P32 decay. Samples which were frozen after incubation for 9 minutes were completely stable.Experiment II. Radioactive B/r bacteria in radioactive growth medium were infected with non-radioactive ( i.e . stable) T2 and incubated for various lengths of time before being frozen and stored in liquid nitrogen, like those of Experiment I. In this case, the infective centers were stable to P32 decay as long as they were frozen before the end of the eclipse period. The T2 progeny phages issuing from the infected bacteria were P32-unstable.Experiment III. Radioactive B/r bacteria in radioactive medium were infected with radioactive ( i.e . P32-unstable) T2 and otherwise incubated and frozen like those of the first two experiments. In this case, the same progressive stabilization, of the infective centers towards inactivation by P32 decay was observed as that found in Experiment I. The ability to yield infective progeny of infected bacteria incubated for 10 minutes at 37°C. before freezing could no longer be destroyed by P32 decay. The progeny issuing from the infected cells were as unstable as the parental phage.These results could be explained by one of three general hypotheses. As vegetative phage begins to multiply, it is possible that: ( a ) there is a high probability that any part of the vegetative phage already duplicated can be saved after its destruction by P32 decay through a process analogous to multiplicity reactivation or, ( b ) there occurs a change in state of the deoxyribonucleic acid (DNA) preliminary to or in the course of its replication that renders it refractory to destruction by P32 decay, or, finally (c) there occurs a transfer of the genetic factors from the DNA of the infecting phage to another substance not sensitive to destruction by P32 decay.
展开▼
