Fe(III) Oxide Reactivity Toward Biological versus Chemical Reduction

Abstract

Initial rates of biological (Shewanella putrefaciens strain CN32, pH 6.8) and chemical (ascorbate, pH 3.0) reduction of synthetic Fe(III) oxides with a broad range of crystallinity and specific surface area were examined to assess how variations in these properties are likely to influence the kinetics of bacterial Fe(III) oxide reduction in heterogeneous natural Fe(III) oxide assemblages. The results indicate that bacterial Fe(III) oxide reduction does not respond strongly to oxide crystal thermodynamic properties (∆G f ) which exert a significant impact on the kinetics of abiotic reductive dissolution. These findings suggest that oxide mineral heterogeneity in natural soils and sediments is likely to affect initial rates of bacterial reduction (e.g. during the early stages of anaerobic metabolism following the onset of anoxic conditions) mainly via an influence on reactive surface site density and that inferences regarding the competitiveness of bacterial Fe(III) oxide reduction as a pathway for organic matter oxidation in anoxic environments cannot be based on assumed thermodynamic properties of the dominant oxide phase(s) in the soil or sediment.

Rapid electron exchange between surface-exposed bacterial cytochromes and Fe(III) minerals

“…This is consistent with the rates (1.1 × 10 3 to 8.5 × 10 3 e·s −1 ) observed here for the transfer of electrons from the interior of proteoliposomes through MtrCAB to externally located Fe(III) oxides. The order of surface area-normalized reactivity for MtrCAB proteoliposomes with the Fe(III) oxides (GT < HT < LEP) is the same as that observed for reduction by S. oneidensis cultures (26,27). LEP is the most reactive owing to higher redox potential and site density; this is reflected equally in reaction rates observed with bacteria and with MtrCAB proteoliposomes.…”

Identification of iron-reducing microorganisms in anoxic rice paddy soil by 13C-acetate probing

“…Apparently, the type and amount of iron oxide amended has a crucial function in controlling the suppression of methane formation. The pre-incubation of the soil had resulted in the reduction of most of the indigenous ferric iron oxides leaving a high concentration of Fe 2 þ at the beginning of the SIP incubation; under these conditions, added ferric iron oxide might have become coated by the indigenously present Fe 2 þ , and thus, reducing the effective iron(III) oxide surface available for microbial reduction (Roden and Urrutia, 2002;Roden, 2003). This might also explain why only little Fe 2 þ formation was observed in the goethite treatment.…”

“…Microorganisms reduced iron mineral phases with low crystallinity such as hydrous ferric oxide and ferrihydrite at higher rate than phases with a higher crystallinity such as goethite in pure culture experiments (Roden, 2003). In soils, not much is known about the identity of iron-reducing bacteria capable of reducing iron mineral phases.…”

Kinetic Study for Compost Production by Isolated Fungal Strains

“…The rate of microbiological reaction comes from studies of the kinetics of microbial reduction of evaluation parameters such as C/N ratio, TOM and others [9]. Thus, to understand the cycling of C/N ratio in the composting systems, there is need to describe the decomposition kinetics and the biodegradability of the substrate involved.…”