On the Species Specificity of the Nucleic Acids of Bacteria 323 



For the past two years DNA and RNA specificity in various bacteria has been 

 studied at our laboratory by A. S. Spirin and G. N. Zaitseva. This group of 

 organisms seemed to us especially suitable for solving the problem of the species 

 specificity of DNA and RNA. Besides this, the works of many investigators on 

 different organisms with respect to nucleic acid composition and their specificity 

 was concerned in most cases either only with RNA or only with DNA, and there 

 are practically no systematic investigations of the composition of both nucleic 

 acids on a number of biological objects. Bacteria are highly convenient material 

 for this purpose. 



The only satisfactory method of determining quahtative changes or differences 

 of nucleic acids at present is the method of determining the quantitative ratios 

 of their nitrogen bases. In our investigation we therefore carried out a com- 

 parative study of nucleic acid composition in the cultures under investigation 

 by the most widely accepted methods of quantitative paper chromatography in 

 combination with ultraviolet spectrophotometry {2, 3, 4]. It should be borne in 

 mind that in most cases nucleic acid composition was studied by various inves- 

 tigators in preparations of these nucleic acids isolated from organisms. The 

 faulty character of this approach with respect to RNA was shown, specifically, 

 by Chargaff 's laboratory, which started the systematic study of RNA composi- 

 tion in toto, i.e., without isolation [5, 6]. The same fact was estabhshed in our 

 laboratory by Zaitseva in studying the RNA composition of Azotobacter [7]. 

 With respect to DNA composition the Hterature is still dominated by data 

 obtained through the study of DNA preparations. We proceeded on the assump- 

 tion that such methods are not sufficiently reUable, owing to the possibly in- 

 complete isolation of the substances, losses suffered in the course of obtaining 

 the preparations, and, in some cases, its degradation, which may result in com- 

 position changes. Therefore, we endeavoured to study the composition of both 

 RNA and DNA directly in the material under investigation, without first 

 obtaining them as preparations. 



The data for Azotobacter were obtained in our laboratory by G. N. Zaitseva; 

 the data for all the other cultures, by A. S. Spirin. 



Before undertaking the study of DNA and RNA composition in various 

 systematic groups of bacteria, we turned our attention to age alteration of DNA 

 and RNA composition. This was all the more important because if the compo- 

 sition of these nucleic acids altered in the course of development, it would have 

 been necessary to carry out a systematic study on cultures in exactly one and the 

 same phase of development. 



Table i shows DNA composition for Escherichia coli I and Azotobacter agile 

 D-22 depending on the age of the culture; Table 2 gives RNA composition for 

 the same cultures. 



It follows from the data presented in Tables i and 2 that the composition of 

 DNA and RNA undergoes no appreciable change in the course of the develop- 

 ment of the cultures studied. These findings, together with other data available 

 in the hterature [5, 8, 9, 10], give us reason to assume the absence of an age 

 specificity of the nucleic acids for a wide range of organisms, at any rate as far 

 as their composition specificity is concerned. 



