TY - JOUR
T1 - Microbial and geochemical features suggest iron redox cycling within bacteriogenic iron oxide-rich sediments
AU - Gault, Andrew G.
AU - Ibrahim, Alexandre
AU - Langley, Sean
AU - Renaud, Robert
AU - Takahashi, Yoshio
AU - Boothman, Christopher
AU - Lloyd, Jonathan R.
AU - Clark, Ian D.
AU - Ferris, F. Grant
AU - Fortin, Danielle
PY - 2011/2/2
Y1 - 2011/2/2
N2 - The geochemistry, mineralogy and microbiology of bacteriogenic iron oxides (BIOS) deposited at a circumneutral groundwater seep were examined to evaluate the biogeochemical controls on the redox cycle of iron in such environments. X-ray diffraction and extended X-ray absorption fine structure (EXAFS) spectroscopy showed that 2-line ferrihydrite dominated (60-70%) the BIOS mineralogy, with more crystalline lepidocrocite and goethite phases comprising the remainder, likely the product of Fe(II)-induced dissolution-reprecipitation pathways. Subsurface porewater profiles displayed an increase in dissolved (<0.2 μm) equilibrium concentrations of Fe(II), also reflected in peaks in HCl-extractable sedimentary Fe(II) at depth, indicative of biological iron reduction. Interestingly EXAFS analysis of sediments collected from such depths revealed little mineralogical change from the surficial BIOS. Dissolved concentrations of Fe(III), likely present as nanoparticulates or organic complexes, also rose with depth. Scanning electron microscopy images of the surface BIOS samples showed a proliferation of sheath structures characteristic of Fe(II)-oxidizing Leptothrix spp. A 16S rRNA clone library obtained from the surficial BIOS included microorganisms closely associated to known Fe(II)-oxidizing (Gallionella spp., Sideroxydans spp.) and Fe(III)-reducing (Rhodoferax ferrireducens and Geothrix fermentans) bacteria. Analysis of subsurface sediment collected from an Fe(III)-reducing horizon revealed a drop in the proportion of β-Proteobacteria, which hosts numerous Fe(II)-oxidizing genera, and a rise in the β-Proteobacteria, home to anaerobic metal-reducing prokaryotes. The recognition of clones with close identity to bacteria intimately involved in complementary iron redox transformations in the same surficial BIOS sediment suggests that microbial oxidation and reduction of iron may be tightly coupled in this, and other, shallow sedimentary environments. © 2010 Elsevier B.V.
AB - The geochemistry, mineralogy and microbiology of bacteriogenic iron oxides (BIOS) deposited at a circumneutral groundwater seep were examined to evaluate the biogeochemical controls on the redox cycle of iron in such environments. X-ray diffraction and extended X-ray absorption fine structure (EXAFS) spectroscopy showed that 2-line ferrihydrite dominated (60-70%) the BIOS mineralogy, with more crystalline lepidocrocite and goethite phases comprising the remainder, likely the product of Fe(II)-induced dissolution-reprecipitation pathways. Subsurface porewater profiles displayed an increase in dissolved (<0.2 μm) equilibrium concentrations of Fe(II), also reflected in peaks in HCl-extractable sedimentary Fe(II) at depth, indicative of biological iron reduction. Interestingly EXAFS analysis of sediments collected from such depths revealed little mineralogical change from the surficial BIOS. Dissolved concentrations of Fe(III), likely present as nanoparticulates or organic complexes, also rose with depth. Scanning electron microscopy images of the surface BIOS samples showed a proliferation of sheath structures characteristic of Fe(II)-oxidizing Leptothrix spp. A 16S rRNA clone library obtained from the surficial BIOS included microorganisms closely associated to known Fe(II)-oxidizing (Gallionella spp., Sideroxydans spp.) and Fe(III)-reducing (Rhodoferax ferrireducens and Geothrix fermentans) bacteria. Analysis of subsurface sediment collected from an Fe(III)-reducing horizon revealed a drop in the proportion of β-Proteobacteria, which hosts numerous Fe(II)-oxidizing genera, and a rise in the β-Proteobacteria, home to anaerobic metal-reducing prokaryotes. The recognition of clones with close identity to bacteria intimately involved in complementary iron redox transformations in the same surficial BIOS sediment suggests that microbial oxidation and reduction of iron may be tightly coupled in this, and other, shallow sedimentary environments. © 2010 Elsevier B.V.
KW - Circumneutral iron oxidation
KW - Fe(II)-oxidizing bacteria
KW - Fe(III)-reducing bacteria
KW - Redox cycling
U2 - 10.1016/j.chemgeo.2010.11.027
DO - 10.1016/j.chemgeo.2010.11.027
M3 - Article
SN - 0009-2541
VL - 281
SP - 41
EP - 51
JO - Chemical Geology
JF - Chemical Geology
IS - 1-2
ER -