116 



MOLECULES, VIRUSES, AND BACTERLV 



centration of dissolved oxygen versus time; we considered the slope of 

 this curve the measure of the oxygen demand. 



As is apparent from the above, we reached the first peak in the 

 oxygen demand curve at the same time that we obtained the minimum 

 in the pH curve. Shortly thereafter the pH begins to rise, and with this 

 rise a very sharp rise in the oxygen demand occurs. A new enzyme 

 system has apparently developed to utilize the acids responsible for 

 the lowering of the pH. As these acids are oxidized, a very high de- 

 mand for dissolved oxygen develops. In fact, the oxygen demand at 

 this stage far exceeds the demand during vegetative growth. During 

 this second rise in the oxygen demand curve and the corresponding 

 rise in the pH curve, we began to observe in the rods morphological 

 changes which were typical of presporulation. Spores themselves do 

 not actually appear until much later. The actual time of onset of sporu- 

 lation is shown in Figure 3. 



We also investigated the nature of the acids released during the 

 early vegetative cell growth. We found that only two acids formed— 

 pyruvic and acetic ( Nakata, 1959 ) . The pyruvic acid appears first and 

 is subsequently converted to acetic acid. This is illustrated in Figures 

 4 and 5. These acids appear quite stable during the period of vegetative 

 cell growth but begin to disappear as the pH begins to rise; presumably 

 it is the oxidation of the acetic acid that creates the high demand for 

 dissolved oxygen just preceding sporulation. Our failure to obtain 



IS) 



UJ 



q: 

 O 



Q. 

 CO 



UJ 



TIME, HOURS 

 Figure 3. Time of sporulation in an active culture of Bacillus cereus T. 



