The role of alkali-cation transport in energy coupling of neutrophilic and acidophilic bacteria: An assessment of methods and concepts

Aerobic acidophilic and neutrophilic bacteria develop similar proton-motive forces across their cytoplasmic membrane and maintain a cytoplasmic pH close to neutrality. These organisms accomplish this by possessing a strongly pH-dependent membrane potential and transmembrane pH difference. The hypothesis of Booth [6] discussed that the transport cycles of the alkali cations K+ and Na+ across the cytoplasmic membrane determine the pH depdendence of the components of the proton-motive force. In addition, the methods are reviewed that are commonly used to determine membrane potential and transmembrane pH difference in bacteria. It is concluded that most of these methods still give crude results. In particular the membrane potential of neutrophilic bacteria cannot be determined with great accuracy.