The Internal‐Alkaline pH Gradient, Sensitive to Uncoupler and ATPase Inhibitor, in Growing Clostridium pasteurianum

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Abstract
The intracellular pH was measured in growing Clostridium pasteurianum with an acid‐base equilibrium distribution method. [14C]Dimethyloxazolidinedione, [14C]methylamine and [14C]acetic acid were used as “ΔpH‐indicators”. During growth the extracellular pH decreased from 7.1 to 5.1; simultaneously the intracellular pH changed from 7.5 to 5.9. Thus the intracellular pH was more alkaline than the extracellular pH by 0.4 to 0.8 pH‐units. This pH gradient (interior alkaline) was abolished by the proton conductor carbonylcyanide m‐chlorophenylhydrazone and the ATPase inhibitor N,N′‐dicyclohexylcarbodiimide. The pH gradient could not be demonstrated in cells depleted of an energy substrate. These results suggest that the pH gradient is formed by an ATPase‐driven extrusion of protons from the cells rather than by a Donnan potential. Growth of the organism was inhibited by low concentrations of both carbonylcyanide m‐chlorophenylhydrazone (5 μM) and dicyclohexylcarbodiimide (5 μM). This finding suggests that the pH gradient is essential for the growing cell as it may be required for substrate accumulation and other types of transport processes.