MetapoietJc Infegrafions 21 



process of lysogenization. 5. dysenteriae [P2] can be lyso- 

 genized by phage P^, and double lysogenics are thus ob- 

 tained. When phage P2 is added to lysogenic 5. dysenteriae 

 [Pi], phage P2 is adsorbed, but it neither develops nor is 

 converted into prophage. A lysogenic S.. dysenteriae [P^] 

 infected with phage P2 survives and remains lysogenic P^. 

 Thus the presence of prophage P^ blocks the development 

 of P2 and its conversion into prophage (2). 



Alferafions of BacferJal Mefabolhm 



A lysogenic bacterium is modified in its ability to re- 

 produce the homologous phages, to reproduce some heter- 

 ologous phages, and to convert a phage into prophage. The 

 responses of a lysogenic bacterium to phages are modified. 

 In this last section we shall discuss cases in which the 

 presence of prophage brings about modification of the 

 bacterial metabolism and which are apparently not re- 

 lated to any known event in the life cycle of bacterio- 

 phage. 



The first and classical example is the synthesis of a spe- 

 cific toxin by Corynebacterium diphtheriae. Only lysogenic 

 strains carrying prophage (3 are toxinogenic, and non- 

 toxinogenic strains, when lysogenized with phage p be- 

 come toxinogenic (3). When the prophage (3 is suppressed 

 in a lysogenic-toxinogenic strain, the toxinogenic power 

 is lost (4). Bacteria lysogenized with any phage y ^re not 

 toxinogenic. Perhaps phages p and y are related, but what- 

 ever the case may be, there is no cross immunity between 

 them. The interesting point is that lysogenic types may 

 be obtained which exhibit a combination of properties of 

 lysogenics P and y; namely, immunity to y, as in the 

 lysogenic y, and toxinogeny, as in lysogenic p (type 2 of 

 Table II). Things happen as if a recombination had taken 

 place between the genetic material of phage P and y (4). 

 Apparently, toxinogeny is controlled not by prophage P 

 as a whole but by a specific part of its genetic material, 



