RESISTANCE TO ULTRAVIOLET LIGHT AS AN INDEX TO 

 THE REPRODUCTION OF BACTERIOPHAGE 



S. BENZERi 



Calijornia Institute of Technology, Pasadena, California 

 Received for publication July 18, 1951 



Infection of a susceptible bacterium by a single phage particle initiates a 

 series of events climaxed, after a time called the latent period, by bursting of 

 the cell and the release of a number (burst size) of replicas of the initial phage. 

 We are here concerned primarily with the intervening process of phage replica- 

 tion which takes place behind the cloak of the cell wall. By prematurely dis- 

 rupting infected cells, Doermann (1948) found that infective phage replicas 

 are already present well before the time at which the bacterium bursts, i.e., 

 about two-thirds of the way through the latent period. At earlier times, however, 

 no plaque-forming particles are recovered, not even the initial phage. Our atten- 

 tion is, therefore, focused upon this "dark" period, during which the infecting 

 phage must undergo some modification, and the key processes of phage repro- 

 duction come to pass. 



Luria and Latarjet (1947) conceived the following experiment in an attempt 

 to use target theory for an analysis of the intracellular developments. It had 

 been shown by Anderson (1948) that a bacterium {Escherichia coli, strain B) 

 could be subjected to rather heavy doses of ultraviolet light and still survive in 

 its ability to support the growth of phage T2. Thus, if one were to infect cells 

 of strain B with single particles of T2 and irradiate the phage-bacterium com- 

 plexes, the survival of infectivity (the ability to release at least one phage particle, 

 thereby forming a plaque) of the complex should be determined by the survival 

 of the phage part. If the irradiation is done immediately after infection, one 

 should obtain the same survival curve for complexes as for the free phage ir- 

 radiated before addition to bacteria, i.e., an approximately exponential or "one- 

 hit" curve. If complexes are allowed to develop to the point where several intra- 

 cellular phage particles are present, the inactivation of the complex requires at 

 least one "hit" in each phage, and a multiple-target survival curve should be 

 obtained. The set of curves for samples irradiated at different stages in the latent 

 period would be expected to resemble the theoretical curves of figure 1. These 

 multiple-target curves, plotted on a semilogarithmic graph, are characterized 

 by asymptotes of constant slope equal to that for the single phage particle. The 

 intercept of the asymptote, extrapolated to zero dose, corresponds to the loga- 

 rithm of the number of targets. 



^ On leave of absence from the Department of Physics, Purdue University. This investi- 

 gation was conducted in part at Oak Ridge National Laboratory and continued while the 

 author was at the California Institute of Technology as a Postdoctoral Fellow of the Atomic 

 Energy Commission, and a Fellow in Cancer Research of the American Cancer Society, 

 recommended by the Committee on Growth. 



Present Address: Institut Pasteur, Paris 15, France. 



Reprinted by permission of the author and the Williams and 



Wilkins Co., from the Journal of Bacteriology, 63 (1), 59-72, 



January, 1952. 



298 



