336 F. JACOB AND E, L, WOLLMAN 



B. Action of Temperate Phages on Bacterial Metabolism 



The action of temperate phages, or their mutants, on sensitive bacteria is 

 very different from that of virulent phages such as T2, T4, and T6. This is 

 not surprising, since it is known that the protein coat of virulent phages, such 

 as T2, has by itself a strong inhibitory effect on all synthesis of sensitive 

 bacteria (French and Siminovitch, 1955), whereas temperate phages inacti- 

 vated with UV light do not even interfere with bacterial growth. "Whether 

 phage development results from infection of sensitive bacteria or from 

 induction of lysogenic bacteria, bacterial growth proceeds without cell 

 division during the latent period of temperate phages (see Tig. 3). The 

 increase in turbidity corresponds to actual syntheses of bacterial substance: 

 oxygen uptake as well as RNA synthesis increase in a manner parallel to 

 bacterial turbidity (Siminovitch and Rapkine, 1952). Not only do normal 

 bacterial syntheses proceed, but induced biosynthesis of enzymatic systems 

 may also be initiated at any time during the latent period (Siminovitch and 

 Jacob, 1952). 



Although bacterial syntheses still proceed during the multiplication of 

 temperate phages, phage syntheses take place preferentially. This is shown 

 by varying the rate of supply of either the carbon or the nitrogen source 

 during phage development (Jacob, 1952b). A decrease in food supply may 

 suppress bacterial growth without affecting phage production. For low 

 supplies, the available metabolite is used exclusively for phage synthesis. 

 Only when the food supply is high enough, does the surplus of metabohte 

 become available for bacterial synthesis. 



C. Genetics of Temperate Phages 



Mutations of temperate phages have been observed in all systems which 

 have been carefully investigated, whether it be with the phages of B. mega- 

 therium (Murphy, 1952; lonesco, 1956), Salmonella (Boyd, 1951; Levine, 

 1957), E. coli (Bertani, 1953a; Weigle, 1953; Jacob and WoUman, 1954; 

 Kaiser, 1955), or of Pseudomonas (Jacob, 1954; Dickinson, 1954). Some 

 mutants differ from the wild type in their plaque morphology, plaque size, 

 or host range, as in the case of virulent phages. Other mutants differ in their 

 lysogenizing power. The most easily recognizable are those which are unable, 

 or almost unable, to lysogenize. These mutants form clear plaques instead of 

 the turbid ones formed by the wild type. They were observed even in the 

 early days of lysogeny (den Dooren de Jong, 1931; Burnet and Lush, 1936) 

 and have since been found in all systems that have been examined. They 

 occur with a rather high frequency (1 in 10^ to 1 in 10*) and different types 

 can be recognized among them. Most of these mutants are unable to multiply 

 on lysogenic bacteria carrying the wild-type prophage. In the rare cases, 



