HR: 1330h
AN: B12C-0804    [PDF]
TI: The Effects of Microbial Fe(III) reduction on Clay Sediment Flocculation and Mineral Transformation
AU: * Kim, J
EM: jkim@nrlssc.navy.mil
AF: Naval Research Laboratory,, Seafloor Sciences, Stennis Space Center, MS 39529 United States
AU: Furukawa, Y
EM: yfurukawa@nrlssc.navy.mil
AF: Naval Research Laboratory,, Seafloor Sciences, Stennis Space Center, MS 39529 United States
AU: Newell, S
EM: snewell@nrlssc.navy.mil
AF: Naval Research Laboratory,, Seafloor Sciences, Stennis Space Center, MS 39529 United States
AU: Daulton, T
EM: tdaulton@nrlssc.navy.mil
AF: Naval Research Laboratory,, Seafloor Sciences, Stennis Space Center, MS 39529 United States
AU: Dong, H
EM: dongh@muohio.edu
AF: Miami University, Department of Geology,, Oxford, OH 45056 United States
AB: This study was undertaken to investigate physicochemical properties of smectite associated with microbial reduction of structural Fe(III). Iron reducing bacterium, Shewanella oneidensis were inoculated with formate as the electron donor and smectite as the sole electron acceptor for the intervals of 3, 12, 24, and 48 hours in anaerobic chamber. The extent of Fe(III) reduction was observed to reach up to 9%. The control, containing microwave radiation heat-killed bacterial cells and M1 media plus formate, was prepared from the same smectite sample. Settling experiments were performed in anaerobic chamber for 1) the bioreduced nontronite samples which contain viable cells and biopolymers secreted by bacteria, with variable incubation time points, and 2) abiotic nonreduced controls having dead cells (no biopolymers). Furthermore, the separate set of incubation was prepared in aerobic condition where the microbial Fe-respiration does not prevail, but viable bacteria produced the biopolymers, and then suspended in a settling column in aerobic condition. Compared with abiotic nonreduced control, Micromeritics Sedigraph measured 2.3-ŸYm increase of mean aggregate size and a 30-times faster average settling velocity in the bioreduced nontronite suspensions. In addition, the aerobically inoculated nontronite (no Fe-respiration) shows a similar aggregate size distribution to that of an abiotic nonreduced control. Significant changes in physical properties of smectite induced by microbial Fe(III) reduction were directly observed using Environmental Cell Transmission Electron Microscope (EC-TEM). Particularly, neoformation of minerals in bioreduced smectite sample indicate that environmental factor such as bacterial activity should be considered as a geological variable for the mineral transformation studies. Neoformed Illite phase was identified in bioreduced smectite sample that challenge the conventional concept of smectite-to-illite transformation with far-reaching implications. In floc architecture, several domains of smectite packets are glued by biopolymers secreted by bacteria, and the aspect ratio (thickness/length) of individual smectite particle increases from 0.11 to 0.18. We suggest that surface chemistry changes (more negatively charged on smectite surface) induced by microbial Fe(III) reduction more likely to promote the flocculation by absorbing the cations which bridge the smectite particles and the biopolymers resulting in the increase of mean aggregate size.
DE: 1045 Low-temperature geochemistry
DE: 1615 Biogeochemical processes (4805)
DE: 3947 Surfaces and interfaces
SC: Biogeosciences [B]
MN: 2003 Fall Meeting