1952] ULTRAVIOLET LIGHT INDEX IN BACTERIOPHAGE 71 



shows multiplicity reactivation with other particles of T2r, and also undergoes 

 genetic recombination with mutants of T2 and other closely related phages. 

 T7, on the other hand, is much smaller in size, spherical in shape, does not appear 

 to have a membrane, and does not show multiplicity reactivation. Whether it 

 undergoes genetic recombination is not known. 



Therefore, the sequence of events in the intracellular development of T2r, 

 which is reflected in the resistance changes, may be characteristic for the mul- 

 tiplication of only certain types of phage. 



We stand to learn a great deal about the growth of T2r by making use of the 

 radiation resistance index. If conditions are suitable for phage development, the 

 index (i.e., the survival of infective centers after a given standard dose of ultra- 

 violet) goes up (or down, in the latter half of the latent period). If, for any reason, 

 phage development is blocked, the index remains constant; its value marks the 

 stage at wliich the block occurs. This makes it possible to study the effect, at 

 any chosen part of the latent period (except near the end), of many factors, for 

 example temperature, growth requirements, and specific chemical inhibitors. 

 The results of these investigations will be reported separately. 



This tool offers promise not only for studying phage growth but for certain 

 problems in bacterial physiology as well. The growth of phage in a bacterium 

 is dependent upon the metabolic well-being of the cell and on its ability to make 

 use of the substrates supplied to it. By infecting the bacterium with a T2r 

 particle and using the radiation resistance index, the metabolic capabilities of 

 the bacterium under particular conditions can be measured. A unique feature 

 of this technique is that one can determine not only the average rate of metab- 

 olism but the distribution of rates (from analysis of the survival curves) among 

 the individual cells in the population. This idea is currently being applied to the 

 problem of the kinetics of enzymatic adaptation in bacteria. 



SUMMARY 



Techniques are described for simultaneous starting and stopping of the growth 

 of bacteriophage in all the host cells of a culture. Using these techniques, a 

 comparison is made of the changes in resistance to ultraviolet of phages T2r 

 and T7 during intracellular growth, following the method of Luria and Latarjet. 



Phage T7 gives results similar to expectations from target theory, while the 

 results with T2r confirm the (anomalous) behavior observed by Luria and 

 Latarjet, indicating that there may be large differences in the modes of repro- 

 duction of different phages. 



The utility of the change in resistance as a tool in studying bacteriophage 

 reproduction and certain problems in bacterial physiology is pointed out. 



REFERENCES 



Anderson, T. F. 1948 The growth of T2 virus on UV killed host cells. J. Bact., 56, 



403-410. 

 Anderson, T. F. 1949 The reactions of bacterial viruses with their host cells. Botan. 



Revs., 15, 464-505. 



310 



