HR: 0830h
AN: B21B-0712    [PDF]
TI: Microbially-mediated Iron Dissolution and the Potential for Radionuclide Redistribution
AU: * Lack, J G
EM: lack@lanl.gov
AF: Los Alamos National Laboratory, Bioscience Division (B2) MS M888, Los Alamos, NM 87545 United States
AU: Maldonado, D
EM: delmaort@yahoo.com
AF: Los Alamos National Laboratory, Bioscience Division (B2) MS M888, Los Alamos, NM 87545 United States
AU: Rivere, T
EM: tes_riv@yahoo.com
AF: Los Alamos National Laboratory, Bioscience Division (B2) MS M888, Los Alamos, NM 87545 United States
AU: Forsythe, J
EM: jforsyth@nd.edu
AF: Los Alamos National Laboratory, Bioscience Division (B2) MS M888, Los Alamos, NM 87545 United States
AU: Boukhalfa, H
EM: hakim@lanl.gov
AF: Los Alamos National Laboratory, Actinide,Catalysis,and Seperations Chemistry (C-SIC) MS J514, Los Alamos, NM 87545 United States
AU: Ruggiero, C
EM: ruggiero@lanl.gov
AF: Los Alamos National Laboratory, Actinide,Catalysis,and Seperations Chemistry (C-SIC) MS J514, Los Alamos, NM 87545 United States
AU: Neu, M
EM: neu@lanl.gov
AF: Los Alamos National Laboratory, Actinide,Catalysis,and Seperations Chemistry (C-SIC) MS J514, Los Alamos, NM 87545 United States
AU: Traina, S
EM: sam.traina@ucop.edu
AF: University of California-Merced, Sierra Nevada Research Institute P.O. Box 2039, Merced, CA 95344 United States
AU: Hersman, L
EM: hersman@lanl.gov
AF: Los Alamos National Laboratory, Bioscience Division (B2) MS M888, Los Alamos, NM 87545 United States
AB: Investigation into microbial iron dissolution and the effects on radionuclides associated with Fe-containing minerals is of significant importance in determining the distribution and fate of actinides (e.g. uranium, plutonium, neptunium) in contaminated environments. Nearly all microorganisms have a metabolic requirement for iron at ~10-7 M for growth and survival. Iron, while abundant, only has a solubility product in the range of 10-39 to 10-44 M Fe that limits its available concentration in the environment to ~10-17 M. Thus, microorganisms are faced with a discrepancy of ~10 orders of magnitude to overcome in acquiring Fe needed for growth. Experiments were performed with two ubiquitous aerobic Pseudomonads (Pseudomonas mendocina and P. putida) to determine their ability to grow on iron-deficient media utilizing insoluble Fe-oxides as well as soluble Fe as their iron sources. Bacterial growth was observed indicating that the bacteria are actively sequestering Fe from the minerals via dissolution mechanism(s). Moreover, different pathways of dissolution used in obtaining iron from different Fe-oxides (ferrihydrite, goethite, and hematite) were quantified by determining siderophore production - an average of ~4-6 x 10-13 mmol x cell-1 when the cells were grown on either of the three minerals studied, while as expected much more siderophore was generated on a per cell basis in the no Fe control, ~15-16 x 10-13 mmol x cell-1, and much less in the readily accessible soluble Fe control (FeEDTA), ~1.5 x 10-13 mmol x cell-1; and reductant production - an average of about ~1-4 x 10-18 mol x cell-1 both cell associated and in the supernatant for hematite, goethite, and FeEDTA, while the cells grown on ferrihydrite produced a much greater amount of reductant per cell, ~14-26 x 10-18 mol x cell-1 and the no Fe control ~6-9 x 10-18 mol x cell-1. These studies of different dissolution mechanisms are not only significant from a geomicrobial view on iron distribution and cycling in the environment, but also important in the possible remobilization/solubilization of radionuclides once considered immobile as bound to/within insoluble Fe-oxides. However, little investigation has been made in aerobic environments contaminated with radionuclides. Radionuclide distribution within these environments is effected by indigenous biogeochemical processes, including the metabolic activities of aerobic microorganisms. Fe is chemically similar to several actinides, two being uranium (U) and plutonium (Pu). It is reasonable then to hypothesize that the metabolic processes of ubiquitous aerobic bacteria, such as P. mendocina and P. putida, driven by the acquisition of Fe, could also significantly effect the distribution of U and Pu in a contaminated environment. Initial studies performed on U(VI)-loaded hematite have indicated that P. mendocina does effect the solubility and distribution of U(VI) during growth of the bacterium in Fe-deficient media with the hematite as its source of iron. Uranium loaded onto the mineral has been measured back in solution to greater extents with bacterial growth cultures present than when no cells are added. Further experiments are now being modified and performed in order to determine the different parameters involved in resolubilization of radionuclides from Fe-oxides
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2003 Fall Meeting