REQUIREMENTS FOR PHAGE PRODUCTION 243 



drolyzing enzyme is a host cell enzyme and is not replaceable by 

 phage enzymes. 



Rather similar evidence is available with respect to the 

 enzymes involved in the synthesis of amino acids. If a culture 

 of E. coli is grown in a medium containing ammonium lactate 

 and salts it will support the growth of a number of phage strains 

 without the addition of amino acids or growth factors. How- 

 ever, if broth-grown bacteria are transferred to the chemically 

 defined medium and then infected with T2 phage the latent 

 period is greatly prolonged and the burst size decreased. An 

 appropriate mixture of amino acids and purine and pyrimidine 

 bases restores phage production by broth grown bacteria (Fowler 

 and Cohen, 1948; Cohen and Fowler, 1948). These experiments 

 show that the rates at which the bacterium can synthesize the 

 raw materials for phage protein and nucleic acid depend on the 

 environment in which the bacteria were grown before infection. 

 Very similar results were observed by Gots and Hunt (1953) in 

 studying the requirements for growth of phage lambda after 

 ultraviolet induction of lysogenic cultures. It was found that for 

 lambda production in broth-grown cells, isoleucine, leucine, and 

 valine are essential. Yet when strain K12 is grown in a glucose- 

 ammonium chloride medium, induced lysis and phage produc- 

 tion occur without the necessity of added amino acids (Borek, 

 1952). Again the nutritional requirements for phage produc- 

 tion are seen to depend on the synthetic capabilities of the host 

 cells as conditioned by their previous environment. In bacteria 

 genetically incompetent to synthesize certain amino acids, phage 

 production does not occur unless the amino acids required for bac- 

 terial growth are included in the medium (Borek, 1952; Burton, 

 1955). Adsorption and invasion by T2 occurs in the absence of 

 the amino acid required for cellular multiplication. However, no 

 phage DNA synthesis occurs, nor does the complex become resist- 

 ant to ultraviolet light (see Chapter XI), until the required amino 

 acid is added. A similar block in development is caused by chlo- 

 ramphenicol (Chapter XV). 



In washed and starved bacteria unknown physiological 



