42 



Essays in Biochemistry 



9KC sonic vibrator for 10 minutes. Less than 0.5 % of the bacteria 

 remained viable after this treatment. After centrifugation at 5000 

 r.p.m., the optical density of the fluids at 260 lm* was determined. 

 It was 0.33, or, only about 20% of the optical density of the medium 

 represented by curve 1, Fig. 2. 



Of course, this argument excludes consideration of the greater specific 

 absorption of nucleic acid fragments after enzymatic depolymerization. 



Low glucose (0.5%) 

 9.20 



8.80 



JS, 8.40 



.o^ 



1.00 



0.80 



Fig. 3. The accumulation of nucleic acid fragments in the culture medium of 

 E. coli K 12 in logarithmic growth phase on low glucose. 



However, incubation at 38° of such sonically disintegrated cells for 

 5 to 10 hours produced only a 15 to 20% increase in optical density. 



The excretion of nucleic acid fragments during starvation was found 

 to be not restricted to lysogenic organisms, for E. coli B and B/r 

 repeated the same pattern. 



Since "abnormal" metabolism is often but an exaggeration of "nor- 

 mal" metabolism, we next studied whether bacteria in logarithmic 

 growth phase excrete any nucleic acid fragments into the culture 

 medium. 



In Fig. 3 the growth curve of a bacterial culture with a limiting 

 glucose concentration of 0.05%, from start through logarithmic phase 

 to declining growth phase, along with the output of ultraviolet-absorb- 

 ing substances (its ultraviolet-absorbing shadow, as it were), are given. 



