194 Discussion 



Alexander: Therefore it is possible that the actual number of cells may 

 also go stepwise. 



Lajtha: Does this cycling imply that the lag-phase which we usually 

 see is only apparent, and that in the first few cycles the number of cells 

 are so few that one does not see them ? We were worried about this some 

 time ago and started cultures with high numbers initially, and then we 

 did not see any lag-phase at all. Furthermore, functionally these 

 bacteria in the so-called lag-phase were sensitive to very small concen- 

 trations of nucleic acid analogues, and to very high concentrations, about 

 50 times that much, in the log-phase. If we started the culture with the 

 same high numbers of bacteria that were present in the log-phase, we 

 had to use again high concentrations of analogues to achieve comparable 

 inhibition of growth. 



Spiegelman: I don't think that all lag-phases are going to be explained 

 on this basis. I do, however, think that this illustrates a rather interest- 

 ing point. Many biologists have used an enormous amount of ingenuity 

 with microbial populations to get phased cultures. In actual fact it 

 may be difficult to avoid them. We just let the thing go to a stationary 

 phase and start it off again and it is phased ; but it does not stay phased 

 very long. We obtain four good cycles and that is about all. 



Gale: How long are your inoculum cells in the stationary phase before 

 rejuvenation? 



Spiegelman: About five hours. 



Krebs: How do the protoplasts obtain energy? Do they respire? 



Spiegelman: Yes, they do respire, but we give them HDP, which seems 

 to be the thing they like the best. 



Krebs: Am I wrong in assuming that this is one of the organisms that 

 does not ferment anaerobically ? 



Spiegelman: It is essentially an aerobic organism. 



Bracket: What do you know about the relationship between this 

 cycling and the time of DNA synthesis ? Is there any correlation between 

 the stage where DNA is being synthesized and the stage where the 

 enzyme is being synthesized? 



Spiegelman: It is very difficult to get really accurate information on 

 that, although we have discovered one thing which may help a lot. 

 You can freeze this thing in whatever stage it is by simply raising the 

 osmotic pressure. I don't know why this should work, but it does. It 

 will freeze it for a matter of hours. Our data suggest that you don't 

 get complete coincidence of the enzyme and DNA-synthesizing plateaus. 



Bracket: Have you studied further the stimulating effect of the 

 removal of DNA ? It is of course rather reminiscent of what happens in 

 Acetabularia after removal of the nucleus. 



Spiegelman: It is tempting to imagine that the removal of the DNA 

 actually decreases the ability of the preparation to synthesize certain 

 proteins. This may give added advantage to the one which is being 

 induced, since the inducer is present, and consequently leads to an 

 increase in its formation. I should like to emphasize that the experiments 

 I have described are not as decisive as yours, because when I say I 

 remove the DNA all I can mean is that I remove the DNA as measured 



