44 



Essays in Biochemistry 



amino acids. However, the concentration of amino acids was too low 

 to contribute significantly to the absorption at 260 ni/t. 



The origin of the nucleic acid fragments in the culture media is 

 obscure. The accumulation may be the result of haphazard "leakage" 

 or of the spillage of surplus synthesis. On the other hand, it may 

 represent the microbial counterpart of the excretion of specific en- 

 dogenous waste products of nitrogen metabolism in metazoa. Such 



High glucose (0.30%) 

 9.20 



1.80 



8.40 



£ 8.00 



7.60 



, 1.00 



7.20 







Fig. 5. The accumulation of nucleic acid fragments in the culture medium of 

 E. colt K 12 in logarithmic growth phase on high glucose. 



an interpretation might be based upon an inversion of Dr. J. Monod's 

 aphorism on comparative biochemistry: "What is true of coli is true 

 of elephants — even more so." 



The final choice from among the above explanations must await the 

 analysis of the excreted nucleic acid fragments from different micro- 

 organisms. 



When the bacteria are cultured with the excess glucose concentration, 

 of 0.3%, customarily used by bacteriologists, the pattern of accumula- 

 tion in the culture medium is completely different (Fig. 5). 



As the declining growth phase in the culture is reached, the output 

 of ultraviolet-absorbing materials is substantially increased until it 

 reaches twice the level of the cultures with the low glucose. The dif- 

 ferent levels of ultraviolet-absorbing substances in the two cases is a 

 reflection of the different conditions which arrest the growth of the 

 bacteria. With the lower glucose concentrations, growth stops upon 



