Redox sensing by Escherichia coli: Effects of copper ions as oxidizers on proton-coupled membrane transport

Escherichia coli is able to grow under anaerobic fermentation conditions upon a decrease in redox potential (Eh). Indeed, upon a transition of E. coli MC4100 wild-type culture to stationary growth phase a decrease in Eh from the positive values (∼+ 100 mV) to the negative ones (∼− 520 mV) was observed, the acidification of the medium and the H2 production were obtained. An oxidizer, copper ions (Cu2+) affected a bacterial growth in a concentration-dependent manner (of 0.1 mM to 10 mM) increasing latent (lag) growth phase duration, delaying logarithmic (log) growth phase and decreasing specific growth rate. Acidification of the medium and the N,N′-dicyclohexylcarbodiimide (DCCD)- and azide-sensitive proton–potassium exchange by bacteria were inhibited, H2 production upon growth and under assays disappeared with Cu2+ (0.1 mM). These effects were observed with hycE but not hyfR and hyc(A–H) mutants and under aerobic conditions. Cu2+ also increased membrane proton conductance. Copper ions are suggested to affect directly the F0F1-ATPase associated with potassium uptake transport system and/or formate hydrogenlyase composed with hydrogenase 4. A role of the F0F1-ATPase in redox sensing under fermentation is proposed.