306 BACTERIOPHAGES 



controlled by the same locus (Streisinger, 1956b). In view of 

 this fact, it is remarkable that the effect of a single host range 

 mutation in T2 does not hav^e a detectable serologic effect 

 (Luria, 1945a; Hershey, 1946a). Lanni and Lanni (1957) 

 have reported serological variation in T5, however. D'Herelle 

 and Rakieten (1935) reported the selection of an antiserum- 

 resistant strain of a staphylococcal phage. Fodor and Adams 

 (1955) obtained segregation and recombination of serological 

 characters in crosses between T5 and the related phage PB. 



h. Other Mutations 



Mutations affecting the ability to lysogenize, usually from 

 temperate to virulent character, are of unusual genetic interest, 

 but these were mentioned above and are discussed in Chapter 

 XIX. The response of lysogenic bacteria to inducing agents 

 also appears to be subject to genetic control by the prophage and 

 Lwoff (1953) describes a probable mutation with respect to this 

 character. 



Ralston and Krueger (1954) obtained variants of a staphylo- 

 coccal phage differing in capacity to undergo host-induced 

 modification. 



Variation in requirements for metal ions have been described. 

 In the case described by Delbriick (1948) calcium is required as a 

 cofactor for adsorption. In other instances calcium serves as a 

 cofactor for injection (Luria and Steiner, 1944). Variation of a 

 staphylococcal phage (Asheshov, 1926) and of a megaterium 

 phage (Wollman and Wollman, 1938) to greater resistance to 

 citrate might be interpreted as a reduced requirement for a co- 

 factor for injection. 



Beumer-Jochmans (1951) described a variant of a staphylo- 

 coccal phage which had acquired the ability to bring about lysis 

 at 44° C. 



Mutation to resistance to proflavine in phages has been re- 

 ported several times (Foster, 1948) (Chapter XV). Resistance 

 can be increased by successive mutational steps. These muta- 



