Effect of positive redox potentials (>+400mV) on the expression of anaerobic respiratory enzymes in Escherichia coli

Abstract

The expression of fumarate reductase and other enzymes of anaerobic respiration in Escherichia coli was studied as a function of the redox potential (E_>h) in the medium. Redox potentials up to +300mV allowed full expression of fumarate reductase (frd) genes. Higher values resulted in decreased expression. The relationship between E_h and expression of frd could be approximated by the Nernst equation, assuming a redox couple with a midpoint potential E₀′=+400mV to 440 mV. At E_h values >+510mV (generated anaerobically by hexacyanoferrate(III)) the degree of repression was the same as that obtained by O₂. Hexacyanoferrate(III) also caused decreased activities of dimethylsulphoxide (DMSO), nitrite and nitrate reductases. Since expression of these enzymes depends on FNR, the gene activator of anaerobic respiratory genes, it is suggested that the function of FNR is controlled by a redox couple of E₀′=+400mV to 440mV.