448 EOLLIN D. HOTCHKISS 



induced in like manner. Each significant case presents a specific trait 

 induced only by DNA coming from a strain already possessing that specific 

 property. Other capsule types were induced in pneumococci.'^^"''^ then 

 analogously in E. coW^ and in Hemophilus influenzae,''^ and subsequently 

 in meningococci.^^ Drug resistance was introduced as a factor transferred 

 by DNA from a resistant strain, and permitting quantitative study of the 

 number of cells transformed.^^ Recently, new transformations have in- 

 cluded biochemically defined traits of sugar fermentation and oxida- 

 tion.''^''^ It has been reported that virulence of crown-gall bacteria for 

 plant hosts can be transmitted to avirulent strains by a DNA-containing 

 preparation.^" Table II shows a list of the transformations reported to be 

 achieved with DNA preparations. Altogether about 21 capsular trans- 

 formations are listed, involving at least 15 different polysaccharide anti- 

 gens, and 3 transformations related to cell surface properties are recorded. 

 In all, at least 30 biochemically distinct characters have been introduced 

 in vitro by bacterial DNA into living cells of the homologous species. 

 Other reports of transfers in vitro of drug sensitivity^''^- or resistances^ -'^ of 

 antigenic^^ and enzymic^^ properties of bacteria induced by bacterial 

 products, and of the transformation of a fibroma into a myxoma virus,^^ -^^ 

 do not in general provide sufficient information to permit a conclusion 

 about the nature of the change or the substances inducing them, or even 

 in some cases whether the change was actually experimentally induced or 

 spontaneous. Certain transformations by nuclease-sensitive agents and 

 penicillin lysates''^ are certainly attributable to DNA, as are presumably 

 certain protein-antigen''^' ^'^ and capsular-antigen''^ ■ ^' shifts obtained in 

 in vivo experiments with pneumococci. Another type of transformation — 

 the transduction of Salmonella — which will be discussed in a later section, 

 appears to be mediated by more complex agents. 



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