Microbially Induced Formation of Fe Carbonates by Metal-Reducing Bacteria Enriched from a CO₂ Repository Candidate Site.

The objectives of this research were to study the microbial diversity of metal-reducing bacteria enriched from sedimentary rock collected from a CO2 repository candidate site and to examine the effect that the bicarbonate concentration had on the iron reduction and biomineralization by the cultures. The enriched metal-reducing bacteria (i.e., JG-3) consisted mostly of Exiguobacterium sp. and Shewanella sp., and the microbial reduction of akaganeite (β-FeOOH), an Fe(III) oxyhydroxide, was examined over 7 days of bacterial cultivation at 30 °C under different concentrations of bicarbonate (0~210 mM). The akaganeite (β-FeOOH) transformed into goethite (α-FeOOH) and magnetite (Fe3O4) in low HCO-3 buffered medium (<70 mM) and was transformed to magnetite and siderite (FeCO3) in high HCO-3 buffered medium (>140 mM). These results indicate that metal- reducing bacteria from a deep subsurface environment reduce and transform an iron oxyhydroxide to siderite (FeCO3) in HCO-3 buffered medium and that microbial iron reduction may accelerate the mineral trapping of CO2 for deep geologic sequestration.