| Abstract
| - Ferrous iron (Fe2+) oxidation by microbial iron matsamples, dominated by helical stalks of Gallionellaferruginea or sheaths of Leptothrix ochracea, was examined.Pseudo-first-order rate constants for the microbial matsamples ranged from 0.029 ± 0.004 to 0.249 ± 0.042 min-1and correlated well with iron content (R2 = 0.929). Rateconstants for Na azide-treated (1 mM) samples estimatedautocatalytic oxidation by iron oxide stalks or sheaths,with values ranging from 0.016 ± 0.008 to 0.062 ± 0.006 min-1.Fe2+ oxidation attributable to cellular activities wasvariable with respect to sampling location and samplingtime, with rate constants from 0.013 ± 0.005 to 0.187 ± 0.037min-1. Rates of oxidation of the same order of magnitudefor cellular processes and autocatalysis suggested thatbacteria harnessing Fe2+ as an energy source compete withtheir own byproducts for growth, not chemical oxidation(under conditions where aqueous oxygen concentrationsare less than saturating). The use of cyclic voltammetry withinthis study for the simultaneous measurement of Fe2+and oxygen allowed the collection of statistically meaningfuland reproducible data, two factors that have limitedaerobic, circumneutral, Fe2+-oxidation rate studies.
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