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The Protonmotive Force and the ∆pH in Spheroplasts of an Acidophilic Bacterium (Thiobacillus acidophilus)
Abstract
At an external pH of 3·0, spheroplasts of the acidophilic bacterium Thiobacillus acidophilus possessed a ∆pH of 2·9 units, a membrane potential of +86 mV, and a protonmotive force of −88 mV. The ultrastructure of the whole cells or spheroplasts showed no unusual features. At given concentrations, SCN− was more effective in collapsing ∆pH in spheroplasts than in whole cells, indicating a lower permeability barrier in the former. However the ∆p values in spheroplasts were very similar to those in the whole cells, and respiratory chain inhibitors a protonophore, and an ATPase inhibitor, alone or in various combinations, were equally ineffective in collapsing ∆pH in whole cells and in spheroplasts. Thus, it is unlikely that the permeability barrier of the outer membrane accounted for the low values of measured ∆p or the ineffectiveness of various agents in collapsing ∆pH in whole cells of this organism; this confirms our previous suggestion that a sizeable ∆pH in T. acidophilus can be maintained by non-chemiosmotic means.
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© Society for General Microbiology, 1982