FERROUS IRON DEPENDENT NITRIC-OXIDE PRODUCTION IN NITRATE REDUCING CULTURES OF ESCHERICHIA-COLI

L-Lactate-driven ferric and nitrate reduction was studied in Escherichia coli E4. Ferric iron reduction activity in E. coli E4 was found to be constitutive. Contrary to nitrate, ferric iron could not be used as electron acceptor for growth. "Ferric iron reductase" activity of 9 nmol Fe2+ mg-1 protein min-1 could not be inhibited by inhibitors for the respiratory chain, like Rotenone, Quinacrine, Actinomycin A, or potassium cyanide. Active cells and L-lactate were required for ferric iron reduction. The L-lactate-driven nitrate respiration in E. coli E4 leading to the production of nitrite, was reduced to about 20% of its maximum activity with 5 mM ferric iron, or to about 50% in presence of 5 mM ferrous iron. The inhibition was caused by nitric oxide formed by a purely chemical reduction of nitrite by ferrous iron. Nitric oxide was further chemically reduced by ferrous iron to nitrous oxide. With electron paramagnetic resonance spectroscopy, the presence of a free [Fe2+ -NO] complex was shown. In presence of ferrous or ferric iron and L-lactate, nitrate was anaerobically converted to nitric oxide and nitrous oxide by the combined action of E. coli E4 and chemical reduction reactions (chemodenitrification).