246 BACTERIOPHAGES 



kill bacteria by specific inhibition of DNA synthesis (Kelner, 

 1953; Herriott, 1951b). Evidently phage infection reverses 

 this inhibition, which suggests that the original damage was con- 

 fined to terminal steps in DNA synthesis. 



Similar conclusions may be drawn from numerous papers on 

 the induction of phage multiplication in lysogenic bacteria by 

 agents normally lethal for bacteria. For instance, a dose of 

 ultraviolet light that kills 70 per cent of a nonlysogenic variant of 

 K12 gives 95 per cent induction of phage growth in the lysogenic 

 strain (Weigle and Delbriick, 1951). 



Penicillin is supposed to interfere specifically with formation of 

 cell wall material in E. coli (Hahn and Ciak, 1957). Concentra- 

 tions of penicillin which prevent bacterial multiplication do not 

 prevent phage growth, although the phage yield is somewhat 

 reduced because of premature lysis (Price, 1947a; Elford, 1948; 

 Krueger, Cohn, Smith, and McGuire, 1948). Such lethal con- 

 centrations of penicillin do not interfere with most of the synthetic 

 abilities of the bacteria because the cells increase markedly in size 

 and in content of protoplasm after treatment with penicillin, 

 much as they do after treatment with ultraviolet light, X-rays, 

 or mustard gas. 



We may conclude that viability of the host cell is not important 

 to the lytic cycle of phage growth provided generalized metabolic 

 processes continue to function. However, interference with 

 energy metabolism or with the source of supply of building 

 blocks results in failure of phage growth. 



These conclusions reached from the study of phage T2 have 

 been informative, but must be regarded as an example of the 

 extreme case. Less severe metabolic effects of infection are seen 

 with other phages (Siminovitch, 1953). Synthesis of DNA and 

 cellular multiplication may be interrupted, but other biosyn- 

 theses, including enzymic adaptation, may continue at a reduced 

 rate. Even synthesis of DNA does not stop completely (Lwoff, 

 1 953) . Evidently if the bacterium is to survive, as in the event of 

 lysogenization by a temperate phage, practically all metabolic 

 effects of infection would have to be reversible. Tl, though little 



