388 BACTERIOPHAGES 



contributed to our understanding of lysogeny cannot be per- 

 formed with colicinogenic bacteria. 



a. Production of Colicin 



The spontaneous production of coHcin by bacteria depends 

 very much on the composition of the culture medium, on the 

 conditions of growth, and on the characteristics of the bacterial 

 strain. It is generally found that more colicin is produced in 

 complex than in simple synthetic media (Heatley and Florey, 

 1946; Jacob, Siminovitch, and Wollman, 1952; Goebel, Barry, 

 and Shedlovsky, 1956). According to the example under study 

 the importance of such factors as aeration (for colicin V) or pH 

 (colicin K) has been stressed. The colicin is sometimes stable 

 in the producing culture, sometimes not. An unfavorable 

 effect of glucose on colicin production has been observed (Gard- 

 ner, 1950). 



The mechanism by which colicin is released by producing 

 bacteria was for a long time unknown. However, the possibility 

 of inducing colicin synthesis in certain colicinogenic strains by 

 exposure to ultraviolet light suggested analogies to induction of 

 lysogenic bacteria that proved fruitful (Jacob, Siminovitch, and 

 Wollman, 1952). 



When a culture of E. coli ML is submitted to small doses of 

 ultraviolet light, the synthesis of colicin starts almost immediately 

 and colicin accumulates inside the cells. After a latent period of 

 about 80 minutes, the bacteria lyse and release colicin into the 

 medium. The general aspects of induced colicin synthesis are 

 therefore very similar, in this case, to those of induction of 

 phage development in lysogenic bacteria (Chapter XIX) . 



In particular, the factors that control induction appear to be 

 identical in both lysogenic and colicinogenic bacteria. Thus 

 both depend on genetic factors : certain bacterial strains are in- 

 ducible, others not. (Inducibility appears to be unrelated to 

 the type, defined by Fredericq's criteria, of colicin produced, 

 however.) In both cases ultraviolet light. X-rays, and nitrogen 

 mustard are effective inducers. In both cases the physiological 



