Dissimilatory bacterial reduction of Al-substituted goethite in subsurface sediments

Abstract

Abstract-The microbiologic reduction of a 0.2 to 2.0 m size fraction of an Atlantic coastal plain sediment (Eatontown) was investigated using a dissimilatory Fe(III)-reducing bacterium (Shewanella putrefaciens, strain CN32) to evaluate mineralogic controls on the rate and extent of Fe(III) reduction and the resulting distribution of biogenic Fe(II). Mössbauer spectroscopy and X-ray diffraction (XRD) were used to show that the sedimentary Fe(III) oxide was Al-substituted goethite (13-17% Al) that existed as 1-to 5-m aggregates of indistinct morphology. Bioreduction experiments were performed in two buffers [HCO 3 Ϫ ; 1,4-piperazinediethansulfonic acid (PIPES)] both without and with 2,6-anthraquinone disulfonate (AQDS) as an electron shuttle. The production of biogenic Fe(II) and the distribution of Al (aqueous and sorbed) were followed over time, as was the formation of Fe(II) biominerals and physical/chemical changes to the goethite.The extent of reduction was comparable in both buffers. The reducibility (rate and extent) was enhanced by AQDS; 9% of dithionite-citrate-bicarbonate (DCB) extractable Fe(III) was reduced without AQDS whereas 15% was reduced in the presence of AQDS. XRD and Mössbauer spectroscopy were used to monitor the disposition of biogenic Fe(II) and changes to the Al-goethite. Fe(II) biomineralization was not evident by XRD. Biomineralization was observed by Mössbauer when sorbed Fe(II) concentrations exceeded a threshold value. The biomineralization products displayed Mössbauer spectra consistent with siderite FeCO 3 (HCO 3 Ϫ buffer only) and green rust . Adsorption of biogenic Fe(II) to accessory mineral phases (e.g., kaolinite) and bacterial surfaces appeared to limit biomineralization. Al evolved during reduction was sorbed, and extractable Al increased with reduction. XRD analysis indicated that neither crystallite size or the Al content of the goethite was affected by bacterial reduction, i.e., Al release was congruent with Fe(II).

Microbial Reducibility of Fe(III) Phases Associated with the Genesis of Iron Ore Caves in the Iron Quadrangle, Minas Gerais, Brazil

“…As a result, mineralogy and surface area of the solids can not completely explain the variability in rates and extents of bioreduction of Fe(III) associated with the various Fe(III)-rich phases ( Figure 4A,B), especially as crystalline hematite was the predominant Fe(III) phase detected by XRD in all of these samples ( Figure 2). Substitutions of chemical species (notably Al) within mineral matrices may modulate the bioreducibility of Fe(III) phases [42,43], though the effect of Al substitution on bioreduction appears to vary, depending on the mineralogy of the Fe(III) phases [44]. However, after preliminary examination of the Fe(III) phases by Mössbauer spectrometry we were unable to detect evidence of differences in Al substitution (data not shown).…”

Transformation of 2-line ferrihydrite to 6-line ferrihydrite under oxic and anoxic conditions

“…Powder XRD patterns and Mössbauer measurements were obtained as described previously Kukkadapu et al 2001). The, JADE+, V5 (Materials Data, Inc., Livermore, California) data analysis software package was used to subtract the XRD spectra of the ammonium-oxalate treated sample from the spectra of the untreated sample.…”

Dissolution of Al-Substituted Goethite in the Presence of Ferrichrome and Enterobactin at pH 6.5

“…Accumulation of Al at the goethite surface during dissolution was thought to block the reactive surface sites, thus decreasing the rate of Fe release. In contrast, the reductive dissolution of a natural Al-goethite (x = 0.17) by Shewanella putrefaciens showed that dissolution was unaffected by Al sorption (Kukkadapu et al 2001). In this latter study, reductive dissolution was thought to occur at sites distant from those of Al precipitation or adsorption.…”

“…Given the potential for Al substitution to influence the dissolution of goethite and other Fe(III) oxides, and thus the supply of bioavailable Fe(III), a growing body of work has explored the rates and mechanisms of dissolution for both natural and synthetic Al-substituted goethites (Cervini-Silva and Sposito 2002;Dominik et al 2002;Ekstrom et al 2010;Kukkadapu et al 2001;Maurice et al 2000).…”