The Biochemistry of Lysogeny 



45 



the exhaustion of the carbon source. The pH of such cultures even 

 after 24 hours of incubation does not fall below 6.4. However, with 

 the high glucose, the pH of the medium at the end of 7 hours is 5.5. 

 The stationary population under these conditions is the result not only 

 of diminished rate of cell division but of an increased death rate. 



The two methods of culture yield similar bacterial densities, but the 

 environment of the bacteria differ. These findings together with those 

 on starving cultures point to the necessity of examining the culture 



so 



_ 60 



Z 40 



20 



12 3 4 5 6 



Hours 



Fig. 6. The kinetics of the development of inaptitude on methionine .starvation. 



Survivors were determined both in the original starvation medium (striped bar) 



and in fresh starvation medium (solid bar). 



fluid in radiobiological studies of microorganisms for, under some con- 

 ditions of culture, the medium may be laden with nucleic acid frag- 

 ments and may have variable screening potency. For example, if 

 E. coli B in logarithmic growth phase is centrifuged, and the cells are 

 resuspended in a sterile filtrate of optical density 1.5 obtained from 

 the experiment represented by curve 1, Fig. 2, and then exposed to 

 30 seconds irradiation from a G.E. 15-watt germicidal lamp at 1 meter 

 distance, the survivors will be 70% higher than in a control in which 

 the bacteria are resuspended in fresh culture medium and irradiated. * 

 However, screening by nucleic acid fragments in the culture medium 

 has practically nothing to do with inaptitude in lysogenic organisms 

 as is shown by the data presented in Fig. 6. In this quantitative study 

 of the development of inaptitude on methionine starvation, the survival 

 of the organisms from the same dose of irradiation in their original 

 starvation medium and in fresh deficient medium was compared. Only 

 after 5 hours of starvation were sufficient amounts of nucleic acid 

 fragments accumulated in the medium to screen the radiation mens- 



