182 A. N. BELOZERSKY AND A. S. SPIRIN 



ferent treatments and which differ drastically from the original bacteria in 

 their morphological, cultural, serological, biochemical, and other char- 

 acters. To this group belong different L-forms, 162, 163 G-forms, 164 ' 165 and 

 alkali-producing forms. 166 ' 167 The question naturally arises, whether the 

 nucleic acids change under such conditions of far-reaching variability. The 

 analysis of the specificity of nucleic acid composition must, in its turn, help 

 to answer the question, to what extent the apparent alterations of the 

 bacterial cell correspond to changes in the nucleic acids that are directly 

 associated with the hereditary apparatus of the cell. 



In our laboratory, studies were performed on the DNA and RNA com- 

 position of some representatives of the intestinal group of bacteria and of 

 their atypical forms produced as a result of experimental variability. 168170 

 The material investigated represented hereditary resistant forms, the so- 

 called "saccharolytically inert" forms (which do not ferment sugars) pro- 

 duced from the intestinal bacteria by various treatments. 166 - 170 They may 

 be divided into two groups differing widely in their properties. One group 

 is represented by the so-called "neutral forms," which show neutral re- 

 action on peptone media in the presence of sugars, and which seem to be 

 identical with those described in the literature as G-forms. Another group 

 is represented by "alkali-producing forms," showing alkaline reaction on 

 the same media. It was shown that the formation of these forms is ac- 

 companied by drastic changes in several properties, such as, morphological, 

 cultural, serological, biochemical characteristics, and resistance to anti- 

 biotics. On the other hand, forms of the same type are exceptionally similar 

 in their properties. 



Comparing these data with those on the DNA composition presented in 

 Table XII, one finds many regular correlations. Thus, all of the original 

 intestinal bacteria are very similar in a number of biological properties and 

 in their resistance to antibiotics; and all of them have a group antigen in 

 common. Their biological similarity is in accord with the similarity of their 

 DNA composition [a slightly marked GC-type, (G + C)/(A + T) = 1.2]. 



162 E. Klieneberger-Nobel, J. Gen. Microbiol. 3, 434 (1949). 



163 E. Klieneberger-Nobel, Bacteriol. Revs. 15, 77 (1951). 



164 P. Hadley, J. Infectious Diseases 60, 129 (1937). 



166 P. Hadley, in "Pathogenic Microorganisms" (W. H. Park and W. Williams, eds.). 

 London, 1939. 



166 D. G. Kudlaj, "Variability of the Bacteria of the Intestinal Group," Medgiz, 

 Moscow, 1954. 



167 D. G. Kudlaj, Zhur. mikrobiol. epidemiol. immunobiol . No. 6, 32 (1954). 



168 A. N. Belozersky, A. S. Spirin, D. G. Kudlaj, and A. G. Skavronskaja, Biokhimiya 

 20, 686 (1955). 



169 A. S. Spirin and A. N. Belozersky, Biokhimiya 21, 768 (1956). 



170 A. S. Spirin, A. N. Belozersky, D. G. Kudlaj, A. G. Skavronskaja, and V. G. Mi- 

 tereva, Biokhimiya 23, 154 (1958). 



