Effect of Oxidation Rate and Fe(II) State on Microbial Nitrate-Dependent Fe(III) Mineral Formation

Abstract

(3,26,34,49,53,56). It has also been observed to occur in diverse ecosystems including activated sewage sludge (37), anoxic aquifer sediments (6,24,26,48), and marine sediments (45). Solid-phase Fe(II) species [including sorbed Fe(II) as well as Fe(II) sulfides, carbonates, and phosphates] often represent a large fraction of Fe(II) in anoxic aquifers (12). Both dissolved and solid forms of Fe(II) are known to be susceptible to anaerobic oxidation (27,33,45,61), with different biogenic Fe(III) (hydr)oxide mineral phases (including goethite, lepidocrocite, ferrihydrite, magnetite, and green rust) produced under similar physical and chemical conditions (11,33,34,48,54). The reason for the previously observed mineralogical differences in biogenic Fe(III) (hydr)oxide phases is unclear, but the chemical form of Fe(II) and the Fe(II) oxidation rate appear to exert control on the mineralogy for abiotically produced Fe(III) (hydr)oxides (19,60).The crystallinity of Fe(III) (hydr)oxide mineral phases strongly influences their susceptibility to microbiological reduction as well as their ability to act as a chemical oxidant (22,28,29,35,44,62). For instance, the poorly crystalline Fe(III) (hydr)oxide ferrihydrite is biologically reduced to a greater extent than the crystalline (and more thermodynamically stable) hematite (29,35,62). Therefore, the mineralogy of Fe(III) (hydr)oxide products of nitrate-dependent Fe(II) oxidation may have a profound impact on the cycling of Fe in anoxic environments.Here, we report on the characterization of a Klebsiella species (designated strain FW33AN) from a nitrate-and radionuclide-contaminated aquifer that is capable of anaerobic, nitrate-dependent Fe(II) oxidation. Strain FW33AN was previously shown to produce goethite by nitrate-dependent Fe(II) oxidation (48), and we show here that the chemical form of Fe(II) substrate and the rate of Fe(II) oxidation influence the mineralogy of biogenic Fe(III) (hydr)oxide products. MATERIALS AND METHODSIsolation of strain FW33AN from FRC groundwater. During push-pull tests to stimulate nitrate and U(VI) reduction at the Oak Ridge Field Research Center (FRC) in Oak Ridge, TN (30), biomass that had accumulated in injection well FW033 was collected, refrigerated, and shipped to the University of Oklahoma where it was stored at 4°C for less than one week. A 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES)-buffered (50 mM, pH 7) solid medium was used that contained 0.8 g/liter NaCl, 1 g/liter NH 4 Cl, 0.1 g/liter KCl, 0.03 g/liter KH 2 PO 4 , 0.2 g/liter MgSO 4 · 7H 2 O, and 0.04 g/liter CaCl 2 · 2H 2 O, vitamins, and trace metals (57). Acetate (30 mM CH 3 COONa) was provided as an electron donor, nitrate (20 mM NaNO 3 ) was the sole terminal electron acceptor, and agar (20 g/liter) was used as a solidifying agent. Plates were prepared under oxic conditions before transfer to an anoxic glovebag (Coy Laboratory Products, Grass Lake, MI) where they equilibrated overnight. Biomass-containing groundwater samples were serially diluted and spread on...

Biomineralization of lepidocrocite and goethite by nitrate-reducing Fe(II)-oxidizing bacteria: Effect of pH, bicarbonate, phosphate, and humic acids

“…Most likely, the broad Fe(III) sextets represent a disordered or amorphous Fe(III)-phosphate solid similar to the one observed to form when BoFeN1 oxidized Fe(II) in a high phosphate content and characterized by scanning transmission X-ray microscopy (Miot et al, 2009a). Phosphate species are expected to affect Fe(III) mineralogy here because they previously have been observed to alter Fe(III) crystallinity during Fe(II) oxidation (Châtellier et al, 2004) and Fe(III) precipitation (Thibault et al, 2009) and have been speculated to influence nitratereducing, Fe(II)-oxidizing bacteria (Senko et al, 2005a). Solid-phase phosphate accumulation was confirmed at the end of the experiment by observing complete removal of phosphate from the aqueous phase in the 0.2 and 1.0 mM total phosphate suspensions.…”

“…The observed Fe(III) mineral diversity may be a result of different mechanisms of enzymatic Fe(II) oxidation, different cell-Fe(III) interactions, and different geochemical solution conditions. Specific factors studied so far include Fe(III) nucleation and templating by cell membranes and exopolymers (Chan et al, 2004;Hallberg and Ferris, 2004;Miot et al, 2009b), rate of Fe(II) oxidation (Senko et al, 2005a), formation of locally acidic environments (Kappler and Newman, 2004;Hegler et al, 2008), and Fe(III) precipitation locations either within, on, or away from cell membranes (Miot et al, 2009b;Schaedler et al, 2009).…”

Microbial reduction of iron(III)-rich nontronite and uranium(VI)

“…1.2 days. Structural Fe(III) in nontronite oxidized biogenic uraninite at rates comparable to uraninite oxidation by poorly crystalline Fe(III) (oxyhydr)oxides (Senko et al, 2005;Ginder-Vogel et al, 2006). The rate of uraninite oxidation was quantified as the rate of soluble U(VI) production according to:…”

The effect of U(VI) bioreduction kinetics on subsequent reoxidation of biogenic U(IV)

“…For instance, rapidly formed minerals may be less crystalline and/or smaller than their relatively slowly formed counterparts (Cornell and Schwertmann, 2003;Fredrickson et al, 2003;Glasauer et al, 2003;van der Zee et al, 2003;Han et al, 2005;Senko et al, 2005a), and these differences in physical characteristics may have a profound effect on their reactivity (Lovley and Phillips, 1987;Deng and Stumm, 1994;Zachara et al, 1998;Glasauer et al, 2003;Roden, 2003;Hansel et al, 2004). In light of this observation, we hypothesized that relatively slow rates of U(VI) bioreduction would give rise to larger and less reactive U(IV) phases that would be more resistant to oxidation than relatively rapidly formed biogenic U(IV) phases.…”