ZINDER AND LEDERBERG 



the FA granules is that they are a 

 heterogeneous population of species 

 each with its own competence— in 

 other words, each carries a "single 

 gene" or small chromosome fragment. 



Regardless of the nature of the FA 

 particles, some mechanism must be 

 postulated for the introduction of the 

 transduced genetic material to the 

 fixed heredity of the recipient cell. 

 Muller's (1947) analysis of type trans- 

 formation in the pneumococcus is 

 apropos here: ". . . there were, in ef- 

 fect, still viable bacterial chromosomes, 

 or parts of chromosomes, floating free 

 in the medium used. These might, in 

 my opinion, have penetrated the cap- 

 suleless bacteria and in part taken root 

 there, perhaps, after having undergone 

 a kind of crossing-over with the chro- 

 mosomes of the host." 



In a preliminary report on the 5^/- 

 monella recombination system (Leder- 

 berg et al., 1951) it was suggested that 

 FA might be related to bacterial L- 

 forms (Klieneberger-Nobel, 1951). 

 The occurrence of swollen "snakes", 

 filtrable granules, and large bodies in 

 response to certain agents is character- 

 istic both of FA and L-forms. Except 

 for the suggestion of viable filter pass- 

 ing granules we have not repeated the 

 reported cycles. The visible agglutin- 

 able granules and the antiserum-in- 

 duced swollen form are not necessary 

 for FA activity. However, this failure 

 to fit all of the elements to a simple 

 scheme may be due to a system more 

 complex than we are now aware. 



The bacteriological literature has 

 numerous reports of results which 

 might be interpreted as transduction 

 (see reviews by Luria, 1947, and 

 Lederberg, 1948). These experiments 

 have been criticized or neglected be- 

 cause of difficulties in their reproduc- 

 tion and quantitization but might now 

 be reinvestigated in light of the find- 

 ings presented. A citation of some of 



237 



the more pertinent ones should suffice 

 at this time. Wollman and WoUman 

 (1925) reported the acquisition of 

 Sabnonella immunological specificity 

 by E. coli via filter passing material. 

 Similar material (which can be ob- 

 tained by phage lysis) has been impli- 

 cated in the change of penicillin re- 

 sistant staphylococci and streptococci 

 to relative penicillin sensitivity (Vou- 

 reka, 1948; George and Pandalai, 

 1949). Shigella paradyse?7teriae (Weil 

 and Binder, 1947) acquired new im- 

 munological specificity when treated 

 with extracts of heterologous types. 

 Boivin (1947) reported a similar 

 change in E. coli. Unfortunately his 

 strains have been lost and confirmation 

 is impossible. Bruner and Edwards 

 (1948) in a report of variation of so- 

 matic antigens of Salmonella grown in 

 the presence of specific serum com- 

 mented on the possibility that bacterial 

 products dissolved in the serum were 

 responsible for the changes. 



These systems, provocative as they 

 are, are insufficiently documented for 

 detailed comparison with Salmonella 

 transduction. The transformations in 

 the pneumococcus (Avery et al., 1944; 

 AicCarty, 1946) and Hemophilus in- 

 fluejizae (Alexander and Leidy, 1951) 

 have been studied more completely. 



The genetic "transformation" of the 

 capsular character of the pneumococ- 

 cus depends on a specific bacterial 

 product (pneumococcus transforming 

 principle, FTP). Originally inter- 

 preted as a directed mutation, it is now 

 regarded as a variety of genetic ex- 

 change (Ephrussi-Taylor, 1950). Thus 

 far transformations have been achieved 

 for the full capsular character (Grif- 

 fith, 1928), a series of intermediate 

 capsular characters (Ephrussi-Taylor, 

 1951), M protein character (Austrian 

 and MacLeod, 1949), and penicillin 

 resistance (Hotchkiss, 1951). As in 

 Salmonella each character is trans- 



