HR: 14:30h
AN: B52C-03 INVITED     [PDF]
TI: X-ray Microprobe Investigations of Elemental Distributions and Concentrations at Mineral-Microbe Interfaces
AU: * Kemner, K M
EM: kemner@anl.gov
AF: Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 United States
AU: Kelly, S D
EM: skelly@anl.gov
AF: Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 United States
AU: O'Loughlin, E J
AF: Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 United States
AU: Lai, B
AF: Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 United States
AU: Maser, J
AF: Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 United States
AU: Cai, Z
AF: Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 United States
AU: Londer, Y
AF: Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 United States
AU: Schiffer, M
AF: Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 United States
AU: Nealson, K
AF: University of Southern California, Science 223, Los Angeles, CA 90089 United States
AB: Understanding the fate of heavy-metal contaminants in the environment is of fundamental importance in the development and evaluation of effective remediation and sequestration strategies. Bacteria and the extracellular material associated with them are thought to play a key role in determining a contaminant's speciation and thus its mobility in the environment. Additionally, the metabolism and surface properties of bacteria can be quite different depending upon whether the bacteria exhibit a planktonic (free-floating) or biofilm (surface adhered) habit. The microenvironment at and adjacent to actively metabolizing cells also can be significantly different from the bulk environment. Thus, to understand the microscopic physical, geological, chemical, and biological interfaces that determine a contaminant's macroscopic fate, the spatial distribution and chemical speciation of contaminants and elements that are key to biological processes must be characterized at micron and submicron lengthscales for bacteria in both planktonic and adhered states. Hard x-ray microimaging is a powerful technique for the element-specific investigation of complex environmental samples at the needed micron and submicron resolution. An important advantage of these techniques results from the large penetration depth of hard x-rays in water. This advantage minimizes the requirements for sample preparation and allows the detailed study of hydrated samples. The objectives of the studies to be presented are (1) to determine the spatial distribution, concentration, and chemical speciation of metals at, in, and near bacteria and bacteria-geosurface interfaces, (2) to use this information to identify the metabolic processes occurring within the microbes, and (3) to identify the interactions occurring near these interfaces among the metals, mineral surfaces, and bacteria under a variety of conditions. We have used x-ray fluorescence microscopy to investigate the spatial distribution of 3d elements in Pseudomonas fluorescens cells in both planktonic and surface-adhered states. We have used x-ray fluorescence spectromicroscopy to investigate the chemical speciation and distribution of Cr that was introduced to these cells as Cr(VI). Additionally, we have used these techniques to identify the distribution of an over expressed cytochrome c7 in individual E. coli. Finally, we have used x-ray fluorescence microscopy to investigate Shewanella oneidensis MR-1 cells adhered to iron oxyhydroxide thin films. The zone plate used in these microscopy experiments produced a focused beam with a cross section (and hence spatial resolution) of 100-300 nanometers. Results from x-ray fluorescence imaging experiments indicate that the distribution of P, S, Cl, Ca, Fe, Ni, Cu, and Zn can define the location of the microbe. Additionally, quantitative elemental analysis of individual microbes identified significant changes in concentration of 3d transition elements depending on the age of the culture and the type of electron acceptor presented to the microbes. These results and a discussion of the use of this technique for identifying metabolic states of individual microbes within communities and the chemical speciation of metal contaminants at the mineral-microbe interface will be presented.
DE: 1065 Trace elements (3670)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting