CHAPTER XIX 



LYSOGENY* 



Although lysogenic bacteria were described many years ago, 

 only recently was the exact nature of the phage-bacterium 

 relationship in such bacteria understood. It is now well es- 

 tablished that lysogeny corresponds to an intimate relationship 

 between the genetic materials of a phage and of a bacterium, 

 which are integrated and reproduce as a single unit. Lysogeny 

 occupies therefore a somewhat unique situation at the crossroad 

 of virology and bacterial genetics. Several reviews have 

 covered the main recent advances in the field (Lwoff, 1953; 

 Jacob, 1954a; Bertani, 1958). 



1. Definition and Occurrence 



Lysogeny is the hereditary property of producing bacterio- 

 phage without infection with external particles. A lysogenic 

 bacterium possesses and transmits to its progeny the capacity 

 to produce phage. 



Soon after the discovery of phage, it was recognized by many 

 workers (Bordet and Ciuca, 1921; Gildemeister, 1921) that 

 filtrates of bacterial cultures isolated from nature often con- 

 tain phages that lyse other "indicator" strains of the same 

 bacterial species or of related species. Two types may be dis- 

 tinguished among such phage-producing strains. In the so- 

 called carrier strains, phage production can be ultimately as- 

 cribed to a population equilibrium between resistant and sen- 

 sitive cells, the latter being constantly infected by free phage 

 particles. These cultures can easily be freed from phage by 

 successive colony re-isolation or by exposure to antiphage serum. 



* Chapter contributed by F. Jacob and E.-L. Wollman. 

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