Escherichia coli maintains pH via the membrane potential

Maintaining intracellular homeostases is a hallmark of life, and Escherichia coli works to maintain several interconnected electrophysiological variables, such as a near-neutral pH and a sufficient electrochemical gradient of protons, the so-called proton motive force (PMF). To generate the latter, E. coli relies on central metabolism to move protons out of the cell, where in its preferred near-neutral extracellular environments this is not enough to achieve reported physiological PMF values. Using mathematical modelling, we predict that E. coli also uses proton-ion antiporters for this purpose. Their principal function, powered by the central-metabolism-enabled proton efflux, is to generate the PMF by moving other ions. Consistently, our model predicts that the PMF determines the range of extracellular pH over which E. coli can maintain both a constant PMF and a neutral intracellular pH. The strength of the PMF sets the maximal/minimal rate at which the antiporters work, and so determines the highest extracellular pH for which the two homeostases hold. We further predict that artificially collapsing the PMF destroys the membrane potential. In support and by concurrently measuring the PMF and pH in individual cells of E. coli, we show that decreasing the PMF’s strength impairs the cells’ ability to maintain pH and that they have negligible membrane potential when there is no PMF. Finally, we use our model to predict the previously reported ranges of extracellular pH for which E. coli expresses three antiporters, by defining their cost through the rate at which they divert protons from generating ATP. Taken together our results suggest a new perspective on bacterial electrophysiology, where cells use antiporters to generate the plasma membrane potential and thus their PMF.