Control of Ferrous Iron Oxidation within Circumneutral Microbial Iron Mats by Cellular Activity and Autocatalysis

Abstract

Ferrous iron (Fe2+) oxidation by microbial iron mat samples, dominated by helical stalks of Gallionella ferruginea or sheaths of Leptothrix ochracea, was examined. Pseudo-first-order rate constants for the microbial mat samples ranged from 0.029 +/- 0.004 to 0.249 +/- 0.042 min(-1) and correlated well with iron content (R2 = 0.929). Rate constants for Na azide-treated (1 mM) samples estimated autocatalytic 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 was variable with respect to sampling location and sampling time, with rate constants from 0.013 +/- 0.005 to 0.187 +/- 0.037 min(-1). Rates of oxidation of the same order of magnitude for cellular processes and autocatalysis suggested that bacteria harnessing Fe2+ as an energy source compete with their own byproducts for growth, not chemical oxidation (under conditions where aqueous oxygen concentrations are less than saturating). The use of cyclic voltammetry within this study for the simultaneous measurement of Fe2+ and oxygen allowed the collection of statistically meaningful and reproducible data, two factors that have limited aerobic, circumneutral, Fe2+ -oxidation rate studies.

β-Lactams and Florfenicol Antibiotics Remain Bioactive in Soils while Ciprofloxacin, Neomycin, and Tetracycline Are Neutralized

“…All experiments were done in triplicate (three independent replicates). Soil slurry experiments were completed in their entirety with the addition of 1 mM sodium azide to limit any potential biological degradation of antibiotics (26). Difficulties with precipitation of sulfadiazine and sulfadimethoxine precluded their analysis by HPLC-UV and we did not have a suitable method for quantifying neomycin by HPLC-UV.…”

Cathodic oxygen reduction catalyzed by bacteria in microbial fuel cells

“…First, oxygen generally competes for the oxidation of inorganic electron donors such as ferrous iron or sulfides. This makes the electron donor no longer available to the microorganisms (Rentz et al, 2007). This effect was occasionally present in the cathodic electron transfer, as the overpotential for direct reduction of oxygen at carbon electrodes is high (Zhao et al, 2006).…”

Direct Adherence of Fe(III) Particles onto Sheaths of Leptothrix sp. Strain OUMS1 in Culture

“…An electron is generated during biogenic oxidation of aqueous-phase Fe(II) to Fe(III) or Mn(II) to Mn(IV) and has long been thought to be essential for autotrophic or mixotrophic metabolism in Leptothrix as an energy source [4,[8][9][10][11][12][13]. The Fe/Mn-oxidizing proteins of L. discophora SS-1 (hereafter referred to as SS-1) were reported to be excreted from bacterial cells in association with exopolymers [8,[14][15][16].…”