32. THE NUCLEIC ACIDS OF MICROORGANISMS 149 



of nucleic acids in each bacterial cell increases proportionally to the rate of 

 increase of growth and cell division, soon attaining its maximum. The 

 amount of nucleic acids in the cells decreases with the slowing down of cell 

 division, and at the end of the growth cycle the nucleic acid content returns 

 to the original level, accompanied by the arrest of the division of the cells. 



Thus, all the data obtained suggested that a correlation does exist be- 

 tween the age, the biological activity, and the rate of growth of the cell 

 on the one side, and its nucleic acid content on the other. 



However, these data concerned, mainly, the dynamics of the over-all 

 nucleic acid content in microbial cells. Further investigations were aimed 

 at the elucidation of the behavior of each nucleic acid, deoxyribonucleic 

 acid (DNA) and ribonucleic acid (RNA), separately. 



It should be noted that a review concerning various quantitative and 

 qualitative aspects of microbial DNA was recently published by Vendrely. 16 



1. Deoxyribonucleic Acid 



The investigations of Caldwell and Hinshelwood 16 carried out on Aero- 

 bacter aerogenes showed that the DNA content per cell remains constant 

 when growing the culture under the most varied conditions, in spite of the 

 variation of the size of the cells, the RNA content, and the rate of growth. 

 Webb 17 has also shown that the growth inhibition of Clostridium welchii by 

 means of magnesium, which brings about a strong modification of the mor- 

 phology of the cells, does not alter the constant DNA content in the cell. 

 The constancy of the DNA content in Hemophilus pertussis, despite changes 

 in the nutritional medium, was shown by Rumanian authors. 18 Further, 

 Ogur et a/. 19 have showm on yeasts the constancy of DNA content and 

 the exact correspondence of this content with the ploidy of yeast cells. 



Similarly, in the analysis of the dynamics of the DNA content in the 

 cell during growth, as a rule great constancy of the DNA content is ob- 

 served in the cells in the logarithmic and stationary phases of growth. 17, 20 ~ 24 



However, when the lag-phase, i.e. the phase preparatory to cellular divi- 



15 R. Vendrely, Ann. inst. Pasteur 94, 142 (1958). 



16 P. C. Caldwell and C. Hinshelwood, J. Chem. Soc. p. 1415 (1950). 

 " M. Webb, Science 118, 607 (1953). 



18 C. Barber and I. Soare, Studii si cercetari inframicrobiol., microbial, si parazitol. 

 8, 617 (1957). 



19 M. Ogur, S. Minckler, G. Lindegren, and C. C. Lindegren, Arch. Biochem. Biophys. 

 40, 175 (1952). 



20 M. L. Morse and C. E. Carter, J. Bacteriol. 58, 317 (1949). 



21 P. Mitchell and J. Moyle, J. Gen. Microbiol. 5, 421 (1951). 



22 B. J. Katchman and W. O. Fetty, J. Bacteriol. 69, 607 (1955). 



23 A. N. Belozersky, G. N. Zaitseva, L. P. Gavrilova, and L. V. Mineyeva, Mikro- 

 biologia 26, 409 (1957). 



24 A. S. Spirin, A. G. Skavronskaja, and A. Pretel Martines, Mikrobiologia 27, 273 

 (1958). 



