244 BACTERIOPHAGES 



changes take place which interfere with phage production. 

 Such studies were reported by Gross (1954a, b) using phage T2 

 and strain K12 of E. coli gro-wn in a glucose ammonium chloride 

 medium. If such cultures were infected with phage T2, they 

 lysed normally with an average burst size of 10 to 20 phage 

 particles per cell. If the bacteria were washed in buffer, starved 

 by aeration, infected, and then returned to glucose medium there 

 was no phage yield. However, if the starved infected bacteria 

 were incubated in broth there was an average burst size of 20. 

 Results similar to those observed in broth were obtained by re- 

 suspending the bacteria in a mixture of amino acids. No single 

 amino acid would suffice for phage production. Evidently 

 starvation of the bacteria causes some physiological damage 

 which renders the cells unfit for phage production in unsupple- 

 mented media. The effect of the damage can be reversed by a 

 suitable mixture of amino acids. 



One may conclude from what information is available that 

 phage production is dependent on the host cell metabolism for 

 energy and for the synthesis of the raw materials of protoplasm 

 such as amino acids and nucleic acid bases if these are not fur- 

 nished in the medium. Therefore, any interference with the 

 energy metabolism or the synthetic enzyme systems of the host 

 cell may be expected to have an effect on phage production. 

 However, it is possible to interfere with bacterial multiplication 

 without affecting phage growth and vice versa, showing that the 

 nutritional requirements for the two processes are not identical. 



d. Synthetic and Energetic Machinery of the Host Cell 



The immediate effects of infection by the virulent phage T2 

 are numerous and dramatic. Cell division is halted and the 

 synthesis of new respiratory enzymes is stopped, but the func- 

 tioning of the existing respiratory apparatus remains unim- 

 paired. The net synthesis of ribonucleic acid and of bacterial 

 deoxyribonucleic acid (l)NA) stops, and the synthesis of phage 

 DNA soon starts (Cohen, 1949). The bacterial nuclei are de- 

 stroyed (Luria and Human, 1950), but the tetrazolium reductase 



