16G A. N. BELOZERSKY AND A. S. SPIRIN 



such great variations were found in higher organisms. 80 Thus, the studies 

 carried out in Chargaff's laboratory have, for the first time, opened special 

 prospects for the study of microorganisms from the viewpoint of bringing 

 out all the regularities and ranges of the species specificity of DNA composi- 

 tion. A large number of data on the DNA composition of microorganisms 

 was obtained some time later through the fundamental work of Ki Yong 

 Lee, Wahl, and Barbu, 130 as well as in the work of our laboratory. 129 • 131 • 146148 

 The data on the DNA composition of gram-negative bacilli are shown in 

 Tables I and II, those for gram-positive bacilli in Table III, and those for 

 cocci in Table IV. 



Analyzing all the data available, first those for bacteria, it should be 

 mentioned that they are confirmed by vast factual material on the regulari- 

 ties which were established by Chargaff for the DNA composition, 14 ' 80 ' 142 

 i.e., A = T, G = C, Pu = Py, and G + T = A + C. The ratio (A + T)/ 

 (G + C) is the index of the composition specificity of DNA which sums 

 up all possible differences in the DNA composition in bacteria. 



The data on the DNA composition in different species of bacteria, which 

 are presented in Tables I-IV, allow the following conclusions: (1) the DNA 

 of bacteria possesses a marked specificity of composition; (2) in closely 

 related species the differences in the DNA composition are usually much 

 smaller than in systematically remote species; (3) the DNA composition 

 of bacteria markedly varies from species to species revealing the diversity 

 of all the types possible: from the pronounced AT-type to the extreme 

 GC-type with all the intermediate ratios. 



Proceeding to the analysis of the differences in DNA composition be- 

 tween different groups of bacteria, there should be noted the absence of any 

 direct connection between the DNA composition with either the gram- 

 positive or gram-negative features of the bacteria, as both groups include 

 species with the DNA of the AT- and the GC-types. 



French authors 130 were particularly interested in the problem as to 

 whether the aerobic or anaerobic character of the bacteria affects the DNA 

 composition in some manner. However, no correlations could be found with 

 respect to this character. 



Analysis of the experimental material on the DNA of bacteria suggests 

 that the DNA composition is most closely related to the systematic position 

 of the organisms. 15 ' 130 ' 146 ' 147 ' 149 Therefore, the investigation of the differ- 



146 A. S. Spirin, A. N. Belozersky, N. V. Shugayeva, and B. F. Vanyushin, Biokhimiya 

 22, 744 (1957). 



147 A. N. Belozersky, N. V. Shugayeva, and A. S. Spirin, Doklady Akad. Nauk S.S.S.R. 

 119, 330 (1958). 



148 G. P. Serenkov and M. V. Pakhomova, Doklady Vyschej Schkoly No. 4, 156 (1959). 



149 A. N. Belozersky, "Nucleoproteins and Nucleic Acids of Plants and Their Bio- 

 logical Significance." Acad. Sci. U.S.S.R., Moscow, 1959. 



