128 BACTERIOPHAGES 



6. Acquisition of Phage Resistance by Lysogenization 



The adsorption of a temperate phage to a susceptible bacterial 

 cell may have either of two results; the bacterium may be lysed 

 with release of phage progeny, or the bacterium may be con- 

 verted to the lysogenic condition, in which the cell and its 

 progeny are permanently endowed with the potentiality of pro- 

 ducing phage. This potentiality is controlled by a latent, non- 

 infectious form of the infecting phage, the prophage, which is 

 carried by lysogenic cells and inherited as part of their genetic 

 make-up. To unify the terminology of lysogenic cultures it has 

 been agreed to use the notation of Williams Smith (1951a). In 

 this system the symbol designating the latent phage is placed in 

 parentheses after the sym.bol designating the bacterial culture. 

 For instance if Pseudomonas aeruginosa strain 13 is lysogenic for 

 phage strain 8, the notation is 13(8). Lysogeny is discussed in 

 Chapter XIX. Only a few facts concerning the effects of lyso- 

 genization on host specificity will be mentioned here. 



It has been noted before that lysogenic bacteria are immune to 

 superinfection by the phage of the type they carry as prophage, 

 although adsorption occurs normally. Burnet and Lush (1936) 

 first realized that the acquisition of phage resistance by lyso- 

 genization is a very different process from the acquisition of 

 resistance by mutation. These authors reported that from 10 to 

 20 per cent of effective contacts between phage and susceptible 

 bacteria resulted in conversion of the bacteria to the lysogenic 

 condition. The conversion was not attributable to genetic 

 heterogeneity in the bacterial population. 



Bertani (1953a), using the terrperate enterophage P2, was 

 able to convert up to 40 per cent of the infected cells of strain Sh 

 oi Shigella dysenteriae to the lysogenic form, Sh(P2). The suscepti- 

 ble strain, Sh, is subject to lysis by the 7 coliphages of the T 

 group, and, of course, by P2. The lysogenic strain, Sh(P2), 

 adsorbs all these phages but is resistant to lysis by P2, T2, T4, 

 T5, and T6. Strain Sh(P2) is lysed by phages Tl, T3, and T7 

 only. In this case conversion of the bacterium to the lysogenic 

 condition results in the acquisition of resistance not only to the 



