Overview

The US Department of Energy must clean up a large number of sites with groundwater and soils polluted with multiple contaminants including heavy metals and radionuclides. Important in situ remediation approaches are being developed to reduce the bioavailability and prevent the further spread of these contaminants via groundwater transport by promoting the activity of microorganisms that will transform the contaminants into insoluble and immobile forms. In order for this approach to work the soil bacteria must be resistant to a wide range of co-contaminant metals such as nickel. Scanning Transmission X-ray Microscopy (STXM) provides the means for studying chemical speciation at the 30-50 nm spatial scale, and can be used to identify spectroscopic signatures of metal resistant mechanisms used by common soil bacteria. We have been using pattern-recognition clustering techniques developed at Stony Brook in a unique way to identify subcellular features in bacteria and to investigate the changes in bacterial chemistry due to interactions with contaminants in their environment. We can determine the functional group responsible for metal binding using the C1s absorption edge spectra. We can quantify the extent of the nickel binding associated with the cell wall, the interior of the cell, and surrounding the cell. In addition, we have been using a segmented detector to record a dark field image simultaneously with the bright field absorption image. Dark field imaging identifies small strongly scattering objects, such as nanoparticles or metal precipitates and can be used in combination with bright field absorption data to determine the spatial distribution of the precipitates in relation to the bacterium.

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9781243569424

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