Life at the Energetic Edge: Kinetics of Circumneutral Iron Oxidation by Lithotrophic Iron-Oxidizing Bacteria Isolated from the Wetland-Plant Rhizosphere

Potential for Microscale Bacterial Fe Redox Cycling at the Aerobic-Anaerobic Interface

“…Emerson and Moyer (1997) found that FeOB do not alter the rate of Fe(III) oxide accumulation in circumneutral pH diffusion-controlled opposing-gradient culture systems, a result verified by our own studies with opposing-gradient FeOB cultures (Sobolev and Roden 2004). In addition, Neubauer et al (2002) showed that FeOB only slightly enhanced (18%) total rates of Fe(II) oxidation over cell-free controls in well-mixed batch reactors. This situation differs from radically from oxidation of Fe(II) at low pH and oxidation of dissolved sulfide at neutral pH, the kinetics of which may be accelerated by a factor of 1,000 or more in the presence of organisms such as Thiobacillus (Singer and Stumm 1972) and Beggiatoa (Jorgensen and Revsbech 1983;Nelson, Jorgensen, and Revsbech 1986), respectively.…”

“…The sediments in the Talladega Wetland (TW) from which strain TW2 was isolated are typical of organic-rich freshwater wetlands (Westermann 1993), characterized by steep gradients of dissolved O 2 and high concentrations of dissolved and solid-phase Fe(II) within mm of the sediment-water interface (Roden and Wetzel 1996;Sobolev and Roden 2002). It is important to acknowledge that our findings with strain TW2 may not necessarily apply to other phylogenetically and physiologically different neutrophilic FeOB, in particular the unicellular FeOB from the γ -subclass of the Proteobacteria that have been isolated from a variety of environments by Emerson and colleagues (Emerson and Moyer 1997;Emerson et al 1999;Emerson and Moyer 2002;Neubauer et al 2002;Weiss et al 2003). For example, the ability of the latter organisms to alter geochemical conditions at the Fe(II)-O 2 interface through production of soluble/colloidal Fe(III) compounds, and/or to grow in close association with FeRB, has not yet been evaluated.…”

“…The involvement of unicellular bacteria in circumneutral Fe(II) oxidation is consistent with the observation of high numbers of unicellular organisms closely associated with Fe(III) oxides in microbial mats present at a groundwater Fe seep in Denmark (Emerson and Revsbech 1994a), and the Fe(III) oxide-rich plaque of aquatic macrophyte roots (Emerson, Weiss, and Megonigal 1999). Studies by Emerson and colleagues (Emerson and Revsbech 1994b;Emerson and Moyer 1997;Neubauer, Emerson, and Megonigal 2002) have clearly demonstrated the potential for chemolithotrophic growth of such organisms coupled to Fe(II) oxidation at circumneutral pH.…”

The Iron Biogeochemical Cycle Past and Present

“…8.1), microbes accelerated Fe(II) oxidation rates from 17 to 75%. Similar extents of microbial contribution to Fe(II) oxidation were found in experiments with iron-oxidisers isolated from the rhizosphere of wetland soils (Neubauer et al, 2002), where a mixed population of microbial mat Fe oxidisers accelerated rates of Fe oxidation by from 40% to 300% (Rentz et al, 2007).…”

Life in the lithosphere, kinetics and the prospects for life elsewhere

“…The basaltic glass has an iron content of approximately 13 per cent. Assuming that aerobic iron oxidation occurs with a yield whereby 0.15 moles of reduced carbon is generated from every mole of Fe 2+ oxidized [46,75] and that a bacterium contains 3.6 × 10 −14 mol C [76], then every 1 m 3 of basaltic glass can theoretically sustain approximately 2.5 × 10 16 iron-oxidizing bacteria. By contrast, the iron concentrations of typical Icelandic streams and rivers are sub-micromolar [77,78].…”