ZINDER AND LEDERBERG 



Unlike S. typhi?nurium, from which 

 the / flagellar phase was derived, phasic 

 variation has not been found in these 

 "hybrids". Experiments are now in 

 progress seeking transduction of other 

 flagellar and somatic antigens. 



The trarisduced cell. Prototrophs 

 produced by transduction \FA (LA- 

 2) on LA-22 1 have been tested for 

 their stability both in vegetative re- 

 production and further transduction. 

 After isolation from the experimental 

 plate they were purified by streaking. 

 Five single colonies were grown in 

 complete broth and plated. Two hun- 

 dred colonies from each were picked 

 and retested on minimal agar: all were 

 prototrophic. The transduced culture 

 was reexposed to FA, and another 

 change was selected (galactose nega- 

 tive to positive). Of some 1,500 colo- 

 nies tested by replica plating, all re- 

 tained the initial transduction to proto- 

 trophv^ 



The transduced culture does not re- 

 lease FA during its growth nor is FA 

 obtainable from it by any other means 

 than those employed for the parent 

 culture. Some difficulty has been en- 

 countered in this respect with the 

 products of intrastrain transduction. 

 They were all resistant carriers of the 

 phage associated with active filtrates 

 and some new phage was needed to 

 evoke FA from them. Phage resistance 

 also reduces the efficiency of iterated 

 transduction, presumably because of 

 impaired adsorption of FA. 



Spontaneous reverse-mutations re- 

 gain the ability to transduce their mu- 

 tant parents as do transduced rever- 

 sions. That is, when a cell goes from 

 A— to A+ by either means, it can 

 again produce A+ agent. Mutation in 

 free FA has not yet been studied. 



The relationship between bacterio- 

 phage ajid FA. Several recent converg- 

 ent lines of evidence point to the iden- 

 tity of FA particles and bacteriophage. 



235 



FA and phage have a common filtra- 

 tion end point; ninety-nine per cent 

 of both are retained by a membrane of 

 A.P.D. 120 niju. They have a common 

 specificity of adsorption on Salmonella 

 serotypes, correlated with somatic 

 antigen XII. In adsorption on 5. 

 typhimuriimi both reach saturation at 

 the same point, and the phage to FA 

 ratio remains constant. During the 

 course of purification, FA and phage 

 remain together. In short term experi- 

 ments, FA and phage are released 

 simultaneously from phage infected 

 bacteria. Electron micrographs show a 

 morphological similarity of particles 

 of proper size. 



That the phage particle can be only 

 a passive carrier of the transductive 

 genetic material is shown by the fol- 

 lowing experiments. From single phage 

 particles grown on bacterial cells there 

 are obtained high titered phage and a 

 population of FA encompassing the 

 entire genotype of the parental cells 

 but capable of only one transduction 

 per bacterial cell. Single phage par- 

 ticles, from this filtrate, can be grown 

 on bacterial cells from the same orig- 

 inal parent but of diff^erent genotype. 

 The FA produced is comparable to the 

 genotype of the secondary donor. 



In the section on the evocation of 

 FA, mention was made of the apparent 

 regeneration of FA by transfer. This 

 was explained as being due to the asso- 

 ciation of FA with phage which served 

 to continuously stimulate its produc- 

 tion. To test this, A-, B + , C+ cells 

 were treated with penicillin. The fil- 

 trate was transferred with the same 

 cells to yield FA (A-, B + , C+) and 

 a phage which could be assayed on 

 these same cells. When added to A-I-, 

 B — , C+ cells (from the same original 

 parent), the FA obtained was A-I-, 

 B-, C-h. All of the B-l- agent was ad- 

 sorbed and lost, and agents paralleling 

 the genotype of the B— cells obtained. 



