LYSOGENY 367 



particles in the form of noninfective units. Every individual 

 of a lysogenic population possesses at least one of these units, 

 for which the term of prophage has been coined (Lwoff and Gut- 

 mann, 1950). The prophage state, in which phage multiplies 

 in lysogenic bacteria without destroying them, must be distin- 

 guished from the vegetative state previously considered in this 

 book, which characteristically leads to the production of mature 

 phage particles and lysis of the cell. Thus in lysogenic bacteria, 

 temperate phages may be encountered in three different states: 

 the prophage state, in which phage multiplies as a noninfectious 

 unit in perfect coordination with the division of the host; the 

 vegetative state, in which phage genetic material is multiplying in- 

 dependently ; shortly to be converted to the infectious state, charac- 

 teristic of resting phage particles. Lysogenization represents the 

 process which converts the genetic material of resting phage 

 into prophage. In lysogenic bacteria phage multiplication 

 proper begins with the transition from the prophage state to the 

 vegetative state and ends with the lysis of the cell. This part of 

 the developmental cycle is presumably identical for virulent 

 and temperate phages. 



Although no direct information concerning the composition 

 of the prophage has as yet been obtained, most of the available 

 evidence points to its deoxyribonucleic nature. The specificity 

 of lysogenization indicates that the prophage must have the 

 same genetic potentialities as the mature particles of the homolo- 

 gous type, in which the genetic specificity appears to be carried 

 by DNA (Hershey and Chase, 1952). Lysogenic bacteria do 

 not contain any detectable antigen of the homologous phage 

 (Miller and Goebel, 1954). The prophage contains the same 

 amount of phosphorus and probably of DNA as the genetic mate- 

 rial of the homologous phage (Stent, Fuerst, and Jacob, 1957). 



Once acquired, the lysogenic character is generally stable. 

 Although spontaneous losses of lysogeny have been reported in 

 some bacterial strains (Dooren de Jong, 1931; Gratia, 1936a; 

 E. S. Anderson, 1951; Clarke, 1952), lysogeny seems to be as 

 stable as any other genetic character. 



