40 



H. O. HALVORSON 



any dipicolinic acid was synthesized, we obtained what appeared 

 to be normal spores. Furthermore, the synthesis of dipicohnic 

 acid was complete, or nearly so, before any of the spores had 

 developed heat resistance. Heat resistance developed approxi- 

 mately an hour after the synthesis of DPA. The development of 

 a spore-like structure (this study would indicate) occurs in- 

 dependent of the synthesis of DPA and this precedes the 

 development of heat resistance. This is shown graphically in 

 Fig. 1. 



100- 



c 

 'o 



-t-J 



CO 



> 

 n 



S50 

 o 



Q. 

 0) 



Ol 



3 4 5 6 

 Time in hours 



10 



Fig. 1. The relationship of heat resistance-total viable count-synthesis of 

 DPA in Clostridium roseiim at 37\ O = Total viable count; • = % spore- 

 stain; A = DPA synthesis; ▲ = heat resistant count. 



When we attempted to repeat this with the aerobe Bacillus 

 cereus, our cultures would lyse about the time they should be 

 producing spores. Investigation showed this was due to a lack 

 of oxygen-i. By using a very heavy inoculum, we developed a 

 condition in which the demand for oxygen exceeded our ability 

 to dissolve oxygen in the water. This prompted us to make a 

 study of the oxygen demand of cultures during various stages of 

 growth and sporulation. The results of this study are shown in 

 Fig. 2. This shows that the oxygen demand curve is bimodal. 

 The first peak in this curve occurs about the time the maximum 

 population of vegetative cells is reached. I should mention that 



