Biogenic iron mineralization accompanying the dissimilatory reduction of hydrous ferric oxide by a groundwater bacterium

Abstract

Dissimilatory iron-reducing bacteria (DIRB) couple the oxidation of organic matter or H 2 to the reduction of iron oxides. The factors controlling the rate and extent of these reduction reactions and the resulting solid phases are complex and poorly understood. Batch experiments were conducted with amorphous hydrous ferric oxide (HFO) and the DIRB Shewanella putrefaciens, strain CN32, in well-defined aqueous solutions to investigate the reduction of HFO and formation of biogenic Fe(II) minerals. Lactate-HFO solutions buffered with either bicarbonate or 1,4-piperazinediethanesulfonic acid (PIPES) containing various combinations of phosphate and anthraquinone-2,6-disulfonate (AQDS), were inoculated with S. putrefaciens CN32. AQDS, a humic acid analog that can be reduced to dihydroanthraquinone by CN32, was included because of its ability to function as an electron shuttle during microbial iron reduction and as an indicator of pe. Iron reduction was measured with time, and the resulting solids were analyzed by X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy (EDS) and selected area electron diffraction (SAED). In HCO 3 Ϫ buffered medium with AQDS, HFO was rapidly and extensively reduced, and the resulting solids were dominated by ferrous carbonate (siderite). Ferrous phosphate (vivianite) was also present in HCO 3 Ϫ medium containing P, and fine-grained magnetite was present as a minor phase in HCO 3 Ϫ medium with or without P. In the PIPESbuffered medium, the rate and extent of reduction was strongly influenced by AQDS and P. With AQDS, HFO was rapidly converted to highly crystalline magnetite whereas in its absence, magnetite mineralization was slower and the final material less crystalline. In PIPES with both P and AQDS, a green rust type compound [Fe (6-x) II Fe x III (OH) 12 ] xϩ [(A 2Ϫ) x/2 ⅐ yH 2 O] xϪ was the dominant solid phase formed; in the absence of AQDS a poorly crystalline product was observed. The measured pe and nature of the solids identified were consistent with thermodynamic considerations. The composition of aqueous media in which microbial iron reduction occurred strongly impacted the rate and extent of iron reduction and the nature of the reduced solids. This, in turn, can provide a feedback control mechanism on microbial metabolism. Hence, in sediments where geochemical conditions promote magnetite formation, two-thirds of the Fe(III) will be sequestered in a form that may not be available for anaerobic bacterial respiration.

Products of abiotic U(VI) reduction by biogenic magnetite and vivianite

“…Magnetite and vivianite formation by S. putrefaciens CN32 has been reported by several researchers (Bell et al, 1987;Kostka and Luther, 1995;Roden and Zachara, 1996;Fredrickson et al, 1998;Dong et al, 2000;O'Loughlin et al, 2007).…”

“…The biostimulation of DMRB will likely lead to biological Fe(III) reduction (Wielinga et al, 2000;Finneran et al, 2002;Anderson et al, 2003;Elias et al, 2004;) and production of sorbed Fe(II) or Fe(II)-bearing minerals as metabolic products. The Fe(II)-bearing phases found include magnetite, siderite, vivianite, ferruginous smectite, and green rust (Bell et al, 1987;Roden and Zachara, 1996;Fredrickson et al, 1998;Zachara et al, 1998;Dong et al, 2000;Roh et al, 2003;O'Loughlin et al, 2007;Komlos et al, 2008;O'Loughlin et al, 2010). Sorbed Fe(II) and the Fe(II)-bearing biogenic phases can provide a reservoir of reducing capacity where reduction of U(VI) may occur due to abiotic interactions .…”

Fe(III) Oxide Reactivity Toward Biological versus Chemical Reduction

“…Strain CN32, isolated from anaerobic groundwater, is capable of carrying out dissimilatory Fe(III) reduction with either lactate or H2 as an electron donor. As previously described (15), the cells were grown aerobically for 16 h on tryptic soy broth (TSB) and then washed twice with sterile anaerobic PIPES buffer prior to use in Fe(III) oxide reduction experiments. The tubes were incubated at room temperature on a rotary shaker (150 rpm) for 3 d. Subsamples were removed daily with a N2-flushed plastic syringe and 18G needle and analyzed for dissolved (0.2 µm-filtered) and total (0.5 M HClextractable) Fe(II) content by Ferrozine analysis.…”

Discrimination based on Gly and Arg/Ser at position 673 between dipeptidyl-peptidase (DPP) 7 and DPP11, widely distributed DPPs in pathogenic and environmental gram-negative bacteria

“…Since most members of group 2 were from the genus Shewanella, we expressed DPP (MEROPS ID: MER096825) from S. putrefaciens to determine the peptidase activity of these members carrying Ser 673 . S. putrefaciens is a typical species of the genus that has been isolated mostly from fish, poultry, and meats, but is also associated with a broad range of human infections [34,35]. It was found that S. putrefaciens DPP specifically cleaved Leu-Asp-and Leu-Glu-MCA, demonstrating its entity as DPP11 (Fig.…”