32. THE NUCLEIC ACIDS OF MICROORGANISMS 175 



in this table as the author did not present figures, restricting himself to the 

 values for the A/T, G/C, and Pu/Py ratios. It should be noted that the 

 findings of two studies 87 ' 148 show the DNA composition of algae to be in 

 full accord with the regularities stated by Chargaff for the base ratios in 

 DNA. The data presented in Table VII show that the DNA of the group 

 of algae, as well as that of the bacteria, exhibits a considerable variability 

 of its composition. One encounters, here, representatives with a marked 

 AT-type of DNA (diatomic) and, on the other hand, others, of which the 

 DNA belongs to a rather marked GC-type (green). The data, however, 

 not being numerous up to the present, do not allow wider conclusions on 

 the species specificity of the DNA composition of algae. 



With respect to the representatives of protozoa, only the data from the 

 paper of Scherbaum on T. pyrijormis maybe quoted. 133 The DNA composi- 

 tion of this organism is as follows (in mole %): guanine, 11.5; adenine, 

 36.6; cytosine, 15.0; and thymine, 36.9. 



In reviewing the data available in the literature, there can be found an 

 extraordinary variability of the DNA composition of microorganisms de- 

 pending upon the species to which they belong. And indeed, the value of 

 the (A + T)/(G -f C) ratio varies from 0.35 in Actinomyces and Sarcina 

 to 2.7 in Clostridium. When comparing these data with those available on 

 the DNA composition in higher organisms, animals 80, 152 and plants, 89 at- 

 tention is drawn to the fact that the variations in DNA composition are, 

 by far, more restricted in higher organisms. Thus, the value of the (A + 

 T)/(G + C) ratio ranges in the representatives of different types of ani- 

 mals 152 from 1.3 to 2.2, whereas in the representatives of different types 

 and families of plants 89 it fluctuates only within the range of 1.1 to 1.7. 

 Besides, unlike the microorganisms, all the DNA of higher forms belong 

 to the AT-type. Such an exceptional diversity of the DNA composition of 

 microorganisms may be connected with the unusual differentiation of lower 

 forms in functional aspects and with the polyphyletic origin of species in 

 this group of living beings. 



All the material analyzed above, shows the taxonomic value of the DNA 

 composition. There are grounds for thinking that the determination of the 

 DNA composition may be useful for the precise definition of the phylo- 

 genetic relations of different groups of bacteria and, perhaps, of other 

 microorganisms as well. 



b. RNA Composition 



In the early stages of the study of RNA composition, the possibility of 

 wide species and even individual variations was not ruled out. 111 This con- 



152 Ki Yong Lee and E. Barbu, Compl. rend. soc. biol. 150, 865 (1956). 



