452 



INACTIVATION OF B.\CTERIOPHAGES 



production of active progeny after each individual had already sustained a "lethal" P^- 

 disintegration, then the rate of inactivation of 0.73 of the plaque formers in this ex- 

 periment should have been significantly reduced over the rate of inactivation of singly 

 infected cells. If, on the other hand, the plaque-forming ability of a multiply infected 

 cell is destroyed as soon as each of the infecting particles has been inactivated by P^'^ 

 decay, then the infective centers in this experiment should have disappeared with the 

 "multiple hit" kinetics indicated in Fig. 4 by a dashed curve. The result of this ex- 

 periment is also shown in Fig. 4. It is seen that inactivation of multicomplexes pro- 

 ceeds at roughly the same rate as inactivation of singly infected bacteria, indicating 

 the absence of any appreciable multiplicity reactivation. Experiments in which P'^ 

 decay was first allowed to take place in free T2 and in which bacteria were then mul- 

 tiply infected with the inactivated phages likewise failed to reveal any multiplicity 

 reactivation. 



Latent Period of Survivors. — Since the efficiency of killing, a, is less than 

 0.1 at low temperatures, it is apparent that after an amount of decay which 



TABLE III 

 Pholoreaclivation of T2 



leaves only a small fraction of the initial phage population still active has 

 taken place under these conditions there have occurred many non-lethal 

 P^2 disintegrations in the survivors. In the case of T2, these survivors, how- 

 ever, exhibit no evident effects of this non-lethal decay and reproduce with 

 normal latent period and burst size. This is in contrast to the survivors of 

 ultraviolet light irradiation whose multiplication is significantly retarded 

 (Luria, 1944). 



Photoreactivation. — T2 bacteriophages inactivated by ultraviolet light can 

 be "photoreactivated" by exposure of bacteria infected with such phages to 

 visible light (Dulbecco, 1949). To examine whether phage inactivated by 

 decay of incorporated P''" could be similarly reactivated by light, assays were 

 made of a radioactive T2 stock before and after decay to 0.0001 of the initial 

 titer, incubating the assay plates either in the dark or under a strong fluo- 

 rescent light. A non-radioactive control stock of T2 was inactivated with ultra- 

 violet light to a survival of 0.000056 and similarly assayed in dark and light. 

 The result of this experiment is presented in Table III, in which it may be seen 



291 



