378 BACTERIOPHAGES 



Specific in the sense that a small fraction of the lambda particles 

 released after induction are able to transfer exclusively the 

 galactose {gal) fermentation markers to which prophage lambda 

 is linked in E. coli K12. The phage material and the adjacent 

 segment of the bacterial chromosome {gal'^ for example) are 

 incorporated as a single unit into a phage particle. Upon ly- 

 sogenization of gal ~ sensitive cells the whole piece is added to the 

 preexisting genome of the cell which becomes a "heterogenote" 

 for the galactose marker, that is, carries both the gal+ and gal~ 

 alleles. Upon induction of such heterogenotes most of the re- 

 sulting phage particles appear to carry the gal+ marker (Weigle, 

 1957). In this process the specific relationship which, in lyso- 

 genic bacteria, ties the prophage to a given region of the bac- 

 terial chromosome may therefore persist during the vegetative 

 state and, after maturation, in infectious phage particles. 



b. Changes in the Bacterium Resulting from Lysogenization 



As a consequence of lysogenization with certain phages, 

 changes may be observed in properties of the host. Such al- 

 terations are phage-specific and demonstrate that, besides 

 conferring ability to produce phage and immunity, a prophage 

 may alter host function in a variety of ways. 



The best studied case is the production of toxin by Coryne- 

 bacterium diphtheriae (Freeman, 1951). Most of the toxinogenic 

 strains are lysogenic and release phage particles which are ac- 

 tive on certain nontoxinogenic strains. Lysogenization of such 

 strains with the phage makes them toxinogenic, and the toxino- 

 genic character can be passed from strain to strain by lysogeniza- 

 tion. The correlation between lysogeny and toxin production 

 is complete. Moreover, this property appears to be restricted 

 to certain temperate phages of C. diphtheriae (Groman and 

 Eaton, 1955; Barksdale, 1955). Recent experiments even 

 suggest that the ability to confer toxinogenesis segregates in crosses 

 between related phages (Groman and Eaton, 1955). 



In other bacterial species the presence of certain prophages 

 can affect properties of the host such as colonial morphology 



