20 Perspectives in Microbiology 



Both bacteriophages 4 and 8 are temperate. But the pres- 

 ence of a given prophage can also prevent the develop- 

 ment of a virulent phage. Thus the lysogenic Shigella 

 dysenteriae perpetuating the prophage P^ does not allow 

 the development of the phages T^, T3, and T7, whereas it 

 allows the development of T2, T4, T5, and Te (2). The 

 situation is the reverse for the lysogenic P2, which allows 

 only the development of T2, T4, T5, and Te. None of the 

 T phages is able to mature in the double lysogenic P1-P2. 

 This block in the reproduction of T phages is suppressed 

 by the action of various inhibitors of the metabolism (7). 

 It is, therefore, due not to the prophage as such, but to an 

 alteration of the bacterial metabolism brought about by 

 the presence of prophage. 



It is interesting to know that Escherichia coli B[P2] 

 allows the development of phage T2, T4, T5, and Te (7). 

 Thus the prophage P2 does not exert the same effect on 

 the bacterial metabolism in E. coli as in 5. dysenteriae. 

 Here again, it seems clear that the properties of a lysogenic 

 system are not "produced" by the prophage, but are the 

 result of the interaction of the genetic material of the pro- 

 phage and of the bacterium. The nonspecific action of a 

 given prophage depends on the genetic constitution of the 

 bacterium. 



Another example of dysgonia has recently been discov- 

 ered {\). E. coli K12 allows the development of phage T2r^ 

 whereas the infection of E. coli K12(X) is not followed by 

 phage production. Moreover, phage T2r does not develop 

 in the lysogenic bacteria in which the development of 

 phage X has been induced by irradiation with ultraviolet 

 light. This is true even if the infection is performed 40 

 minutes after irradiation, that is to say, after the onset of 

 the vegetative phase of phage h The conclusion is that the 

 altered response of the lysogenic bacteria is due not to the 

 prophage as such, but to a modified state of the bacterium 

 brought about by the prophage. 



The presence of a given prophage may also block the 



