376 BACTERIOPHAGES 



defective bacteria is nevertheless demonstrated by the fact 

 that they exhibit the same immunity pattern as normal lysogenic 

 cells. 



In defective strains some lesion of the lysogenic system pre- 

 vents the formation of mature particles. This lesion is generally 

 located on the prophage, since defective bacteria first induced 

 by ultraviolet light and then infected with an homologous phage 

 release a normal burst. By infection with genetically marked 

 phages, it is even possible to localize the defect in the genetic 

 linkage system of the phage. After irradiation, prophage de- 

 velopment may be initiated but one of the steps involved in 

 phage formation, such as maturation, is blocked (Jacob and 

 Wollman, 1956). In some strains, defective bacteria induced 

 by ultraviolet light and infected with homologous phages may 

 release, in addition to normal particles, defective particles which, 

 upon infection of sensitive cells, are able to establish new defec- 

 tive systems (Appleyard, 1956). 



A defective lysogenic bacterium oflfers, therefore, the remark- 

 able example of a phage genetic material that can be perpetu- 

 ated only in the prophage state, restrained by genetic defects 

 from producing infectious particles. Analysis of such strains 

 is likely to yield new information about some of the steps in- 

 volved in phage production. 



8. Lysogeny and Bacterial Genetics 



Lysogenization of sensitive bacteria with a temperate phage 

 results in the appearance of new properties of the host, immunity 

 and phage production, which express phenotypically the pres- 

 ence of a prophage. In most cases, these two properties are 

 the only detectable differences between lysogenic and nonlyso- 

 genic derivatives of the same strain, which otherwise exhibit 

 the same growth rate and the same biochemical potentialities. 



In the last years, however, it has been shown that in some cases 

 temperate phages and lysogeny may modify the genetic potential- 

 ities of the host bacterium. On the one hand, in the so-called 

 transduction process, certain phages can carry pieces of genetic 



