Role of humic-bound iron as an electron transfer agent in dissimilatory Fe(III) reduction

The dissimilatory Fe(III) reducer Geobacter metallireducens reduced Fe(III) bound in humic substances, but the concentrations of Fe(III) in a wide ran ge of highly purified humic substances were too low to account for a signif icant portion of the electron-accepting capacities of the humic substances. Furthermore, once reduced, the iron in humic substances could not transfer electrons; to Fe(III) oxide. These results suggest that other electron-acc epting moieties in humic substances, such as quinones, are the important el ectron-accepting and shuttling agents under Fe(III)-reducing conditions.