Generation of a Membrane Potential by One of Two Independent Pathways for Nitrite Reduction by Escherichia coli

A set of four isogenic Escherichia coli strains has been constructed in which all possible combinations of NADH- and formate-dependent nitrite reductases are active or inactive. Each pathway can be inactivated genetically without a corresponding loss in the other activity: the two pathways are therefore biochemically independent. The generation of a membrane potential during nitrite reduction by formate has been demonstrated using an ion-selective electrode specific for a lipophilic cation. The observed energy conservation results, at least in part, from the ability of formate dehydrogenase in E. coli to pump protons.