THE FORMATION OF SPORES BY BACTERIA 123 



magnesium, calcium, iron, or copper, but less firmly than zinc, cobalt, 

 or nickel ions. In the light of these results, we also tried versene. Ver- 

 sene, added to the extent of 1.5 mg. per ml., also interferes with sporu- 

 lation, but the effect of the versene can be overcome by doubling the 

 concentrations of the minerals normally present in the growth medium. 

 A general chelating agent such as versene must therefore have a dif- 

 ferent effect from the a-picolinic acid. If a-picolinic acid is producing 

 its effect through a chelating action, it must have a rather specific 

 effect upon some special mineral. It would be interesting to pursue this 

 further, but in view of other interesting problems we have not taken 

 the time to do so. 



As other possible inhibitors of sporulation we have tried the esters 

 of acids in the TCA cycle. The results are indicated in Table V. In this 



TABLE V 

 Effects of Some Esters on Sporulation of Bacillus Cereus T. 



table, failure to get spores shows that the ester is serving as an inhibi- 

 tor, whereas a normal spore crop shows that no such inhibition takes 

 place. Ethyl pyruvate, diethyl succinate, ethyl malonate, and diethyl 

 oxalacetate inhibited sporulation, but ethyl acetate, triethyl citrate, 

 ethyl succinate, diethyl L-glutamate, ethyl formate, and ethyl propion- 

 ate did not. 



Figure 8 shows the effect produced by ethyl malonate. It is obvi- 

 ous from this that ethyl malonate behaves differently than a-picolinic 

 acid. This inhibitor prevents sporulation whether it is added before the 

 pH begins to rise or afterward. This inhibitor, therefore, probably does 

 not interfere with the formation but instead interferes with the function 

 of some essential enzyme. With this inhibitor, the pH rises for a while 

 as if the culture were normal but finally falls to the low level produced 

 with a-picolinic acid. We know from other carefully controlled experi- 



