Inhibition of Aconitase by Chelation of Transition Metals Causing Inhibition of Sporulation in Bacillus subtilis

Abstract Sporulation of Bacillus subtilis is inhibited by low concentrations (l1 mm) of α-picolinic acid, quinaldic acid, o-phenanthroline, and dipyridyl, all agents that chelate transition metals. High concentrations (g1 mm) of these agents also inhibit growth and cause cell lysis. In the presence of the chelating agents, 14C-glutamate produces the accumulation of citrate and 14C-glucose that of fructose 1,6-diphosphate, indicating the inhibition of both aconitase and aldolase in vivo. This finding is in agreement with the noncompetitive inhibition observed for the two metal-dependent enzymes in vitro which results from the removal of metal ions by the chelating agents. The strongest effect on the cellular metabolism is caused by the inhibition of aconitase, as follows from the measurement of 14C-uracil incorporation into acid-precipitable material in the presence of ribose, glutamate, or citrate. These findings and the fact that aconitase mutants can grow but not sporulate in nutrient sporulation medium are sufficient reasons for the conclusion that α-picolinic acid, quinaldic acid, o-phenanthroline, and dipyridyl specifically inhibit sporulation because they inhibit aconitase. At the end of exponential growth, aconitase is derepressed or induced even when the chelating agents are present in concentrations affecting sporulation.