COLICINS AND OTHER BACTERIOCINS 389 



conditions of the bacteria, both before and after exposure to in- 

 ducing agents, are important. Finally, bacterial metabolism 

 during the latent period following induction is similar in both 

 systems. After ultraviolet induction of either colicinogenic or 

 lysogenic bacteria, bacterial growth continues, respiratory en- 

 zymes are formed, ribo- and deoxyribonucleic acids are syn- 

 thesized, and superinfecting virulent phages are able to multiply, 

 until the time of lysis approaches. 



Induction of colicin synthesis has been confirmed by Fredericq 

 (1954b) and by Hamon and Lewe (1955). They found, how- 

 ever, that after exposure to ultraviolet light of a number of in- 

 ducible colicinogenic strains, release of the colicin was not ac- 

 companied by visible lysis of the culture. Whether always ac- 

 companied by lysis or not, colicin synthesis brings about the 

 death of the productive cells. Thus, in the same way that the 

 expression of lysogeny is lethal for lysogenic bacteria, the expres- 

 sion of colicinogeny appears to be a lethal process. Both ca- 

 pacities can only be perpetuated in potential form. 



/;. Genetic Determination of Co/icinogeny 



The ability to produce a colicin is a hereditary property of a 

 bacterial strain. Colicinogeny is very stable, and no instance 

 of the loss of this character has been reported. Moreover, 

 colicinogenic bacteria are in general immune to the type of 

 colicin they produce. The problems raised by the mode of in- 

 heritance of colicinogeny are therefore very similar to those 

 raised by the hereditary transmission of lysogeny. There must 

 exist, in colicinogenic bacteria, specific structures endowed with 

 genetic continuity that confer upon the bacteria the capacity to 

 produce a colicin. Colicins being noninfectious, the only possible 

 approach to the problem of genetic determination seems to lie 

 in genetic analysis by bacterial intercrosses. 



It was found by Fredericq that ability to produce a colicin 

 may be transferred from a colicinogenic to a noncolicinogenic 

 strain in mixed cultures. Different types of colicins are thus 



