HR: 1340h
AN: B13A-1037    [Abstracts]
TI: Effects of Cobalt on Manganese Oxidation by Pseudomonas putida MnB1
AU: * Pena, J
EM: jpena@nature.berkeley.edu
AF: Department of Civil and Environmental Engineering, 631 Davis Hall University of California, Berkeley , Berkeley, CA 94720
AU: Bargar, J
EM: bargar@slac.stanford.edu
AF: Stanford Synchrotron Radiation Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025
AU: Sposito, G
EM: gsposito@nature.berkeley.edu
AF: Department of Civil and Environmental Engineering, 631 Davis Hall University of California, Berkeley , Berkeley, CA 94720
AB: The oxidation of Mn(II) in the environment is thought to occur predominantly through biologically mediated pathways. During the stationary phase of growth, the well-characterized freshwater and soil bacterium Pseudomonas putida MnB1 oxidizes soluble Mn(II) to a poorly crystalline layer type Mn(IV) oxide. These Mn oxide particles (2 - 5 nm thickness) are deposited in a matrix of extracellular polymeric substances (EPS) surrounding the cell, creating a multi-component system distinct from commonly studied synthetic Mn oxides. Accurate characterization of the reactivity of these biomineral assemblages is essential to understanding trace metal biogeochemistry in natural waters and sediments. Moreover, these biogenic oxides may potentially be used for the remediation of surface and ground waters impacted by mining, industrial pollution, and other anthropogenic activities.
In this study, we consider the interactions between Co, P. putida MnB1, and its biogenic Mn oxide. Cobalt is a redox-active transition metal which exists in the environment as Co(II) and Co(III). While Co is not generally found in the environment at toxic concentrations, it may be released as a byproduct of mining activities (e.g. levels of up to 20 μM are found in Pinal Creek, AZ, a stream affected by copper mining). In addition, the radionuclide ⁶⁰Co, formed by neutron activation in nuclear reactors, is of concern at Department of Energy sites, such as that at Hanford, and has several industrial applications, including radiotherapy.
We address the following questions: Do high levels of Co inhibit enzymatic processes such as Mn(II) oxidation? Can the multicopper oxidase enzyme involved in Mn(II) oxidation facilitate Co(II) oxidation? Lastly, does the organic matter surrounding the oxides affect Co or Mn oxide reactivity? These issues were approached via wet chemical analysis, synchrotron radiation X-ray diffraction (SR-XRD), and extended X-ray absorption fine structure (EXAFS) spectroscopy. In the presence of both Mn (1 mM) and Co (10-40 μM), Mn oxidation proceeded as it does in the absence of Co; SR-XRD data did not indicate the formation of a separate Co oxide phase, and EXAFS data showed that Co is incorporated into the biooxide structure as Co(III). In the absence of Mn, Co oxide formation was not observed; EXAFS data showed that Co remains as Co(II) and is complexed to cells or EPS. While it cannot be ascertained that Co(II) oxidation and incorporation into the bioxides is completely abiotic, Co(II) is not oxidized by P. putida MnB1 in the absence of Mn.
DE: 0409 Bioavailability: chemical speciation and complexation
DE: 0418 Bioremediation
DE: 0419 Biomineralization
DE: 0448 Geomicrobiology
DE: 0463 Microbe/mineral interactions
SC: Biogeosciences [B]
MN: Fall Meeting 2005