Mechanisms of Fe Biomineralization Induced By Dissimilatory Iron Reduction
EMSL Project ID
2460
Abstract
Iron minerals are ubiquitous in nature and play a critical role in the geochemical cycling of trace elements. In particular, iron oxides serve as potent sorbents and repositories for nutrients and contaminants; they are also terminal electron acceptors in microbial respiration. Ferrous iron solid phases observed in laboratory batch (closed) systems following microbial respiration of ferrihydrite under varying environmental conditions include siderite, magnetite, vivianite, and green rust. The supply rate and resulting aqueous concentrations of ferrous iron are hypothesized to be the controlling factors in resultant biomineralized solids. Here we test this hypothesis and investigate mechanisms of Fe biomineralization within closed (batch) and open (column) systems containing ferrihydrite. Both abiotic (addition of aqueous Fe(II) to ferrihydrite) and biotic (dissimilatory iron reduction of ferrihydrite) experiments were conducted to determine the role of bacteria in biomineralization pathways. Solids are characterized using x-ray absorption spectroscopy. Spatial relationships between minerals and microbes within the biotic systems were resolved previously using transmission electron and scanning electron microscopies in collaboration with Alice Dohnalkova at the Environmental Molecular Science Laboratory (EMSL), Pacific Northwest National Laboratory. Within both abiotic and biotic systems, ferrihydrite converts to goethite and magnetite, with the resulting phase governed, in large part, by Fe(II) concentration. Within biotic systems, goethite forms homogenously throughout the column within 2 days of ferrihydrite reduction. The concentration of magnetite, however, increases upgradient corresponding to Fe(II) concentrations. While Fe(II) concentrations decrease over time, magnetite continues to precipitate within the column suggesting that crystal growth rather than nucleation is the dominant mechanism. Similarly, in abiotic batch experiments, magnetite forms only at higher Fe(II) concentrations while goethite concentrations are equivalent throughout a range of aqueous Fe(II) levels. Although goethite precipitation terminates upon formation of magnetite, goethite concentrations continue to increase in regions lacking magnetite nucleation. Thus, within both biotic and abiotic systems, the conversion of ferrihydrite to goethite appears to be impeded by the nucleation and precipitation of magnetite. The abiotic conversion of ferrihydrite to goethite and magnetite suggests that production of biomineralized solids following microbial reduction may proceed through similar abiotic mechanisms (dissolution/precipitation or solid-state conversion). Accordingly, biomineralization pathways may proceed through a coupled abiotic-biotic pathway where bacteria act solely as the source and control of Fe(II) concentrations while secondary mineralization occurs through purely abiotic means. However, relationships between the ferrihydrite and secondary precipitates within the abiotic system must be investigated. As such, we propose to further collaborate with Alice Dohnalkova in using transmission electron microscopy to investigate whether the precipitation mechanisms within the abiotic systems are equivalent to those in the biotic systems and definitely determine the role of bacteria in secondary mineralization.
Project Details
Project type
Exploratory Research
Start Date
2002-02-21
End Date
2003-01-29
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Competing Fe(II)-Induced Mineralization Pathways of Ferrihydrite
Dohnalkova A, CM Hansel, YA Gorby, and S Fendorf. 2004. "Electron Microscopy Evaluation of the Role of Dissimilatory Metal-reducing Bacteria in Biomineralization Pathways." Microscopy and Microanalysis 10(suppl 2):1538-1539.
Hansel CM, SG Benner, J Neiss, A Dohnalkova, RK Kukkadapu, and S Fendorf. 2003. "Secondary Mineralization Pathways Induced by Dissimilatory Iron Reduction of Ferrihydrite Under Advective Flow." Geochimica et Cosmochimica Acta 67(16):2977-2992.
Structural and compositional evolution of Cr/Fe solids after indirect chromate reduction by dissimilatory iron-reducing bacteria