Interconversion of components of the bacterial proton motive force by electrogenic potassium transport

Abstract

The influence of K+ ions on the components of the transmembrane proton motive force (.DELTA.~.mu.H+) in intact bacteria was investigated. In K+-depleted cells of the glycolytic bacterium Streptococcus faecalis the addition of K+ ions caused a depolarization of the membrane by .apprx. 60 mV. Since the depolarization was compensated for by an increase in the transmembrane pH gradient (.DELTA.pH), the total proton motive force remained almost constant at .apprx. 120 mV. Half-maximal changes in the potential were observed at K+ concentrations at which the cells accumulated K+ ions extensively. In EDTA-treated, K+-depleted cells of Escherichia coli K-12, the addition of K+ ions to the medium caused similar though smaller changes in the components of .DELTA.~.mu.H+. Experiments with various E. coli K-12 K+ transport mutants showed that for the observed potential changes the cells required either a functional TrkA or Kdp K+ transport system. The inward movement of K+ ions via each of these bacterial transport systems is probably electrogenic. Consequently, K+ ion influx leads to a depolarization of the membrane, which in its turn allows the cell to pump more protons into the medium.