Isolation and Microbial Reduction of Fe(III) Phyllosilicates from Subsurface Sediments

• Published in: Environmental science & technology 2012-11, Vol.46 (21), p.11618-11626
• Main Authors: Wu, Tao, Shelobolina, Evgenya, Xu, Huifang, Konishi, Hiromi, Kukkadapu, Ravi, Roden, Eric E
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Bicarbonates - chemistry; Biological and medical sciences; Chemical compounds; Citric Acid - chemistry; Earth sciences; Earth, ocean, space; Exact sciences and technology; Ferric Compounds - chemistry; Ferric Compounds - isolation & purification; Ferric Compounds - metabolism; Fundamental and applied biological sciences. Psychology; Geobacter - metabolism; Geologic Sediments - chemistry; Geologic Sediments - microbiology; Hydrogen Peroxide - chemistry; Iron; Marine and continental quaternary; Oxalic Acid - chemistry; Oxidants - chemistry; Oxidation; Oxidation-Reduction; Sediments; Silicates - chemistry; Silicates - isolation & purification; Silicates - metabolism; Soils; Spectrum analysis; Sulfates - chemistry; Surficial geology; Synecology; Terrestrial ecosystems
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es302639n

Fe(III)-bearing phyllosilicates can be important sources of Fe(III) for dissimilatory microbial iron reduction in clay-rich anoxic soils and sediments. The goal of this research was to isolate Fe(III) phyllosilicate phases, and if possible, Fe(III) oxide phases, from a weathered shale saprolite sediment in order to permit experimentation with each phase in isolation. Physical partitioning by density gradient centrifugation did not separate phyllosilicate and Fe(III) oxide phases (primarily nanoparticulate goethite). Hence we examined the ability of chemical extraction methods to remove Fe(III) oxides without significantly altering the properties of the phyllosilicates. XRD analysis showed that extraction with acid ammonium oxalate (AAO) or AAO in the presence of added Fe(II) altered the structure of Fe-bearing phyllosilicates in the saprolite. In contrast, citrate-dithionite-bicarbonate (CDB) extraction at room temperature or 80 °C led to minimal alteration of phyllosilicate structures. Reoxidation of CDB-extracted sediment with H2O2 restored phyllosilicate mineral d-spacing and Fe redox speciation to conditions similar to that in the pristine sediment. The extent of microbial (Geobacter sulfurreducens) reduction of Fe(III) phyllosilicates isolated by CDB extraction and H2O2 reoxidation (16 ± 3% reduction) was comparable to what took place in pristine sediments as determined by Mossbauer spectroscopy (20 ± 11% reduction). These results suggest that materials isolated by CDB extraction and H2O2 reoxidation are appropriate targets for detailed studies of natural soil/sediment Fe(III) phyllosilicate reduction.