9706382 Banfield The proposed research will investigate the inorganic and biological mechanisms by which layer silicates are weathered, with implications for geochemical cycles, soil fertility, and plant nutrition. Specifically, work will focus on interactions between biotite, chlorite, muscovite, and rhizosphere microorganisms and the reactions that convert these minerals to clays. This work builds on our previous studies of inorganically and biogeochemically mediated alteration of chain silicates and extensive studies of layer silicate structures, microstructures, chemistry, and reaction mechanisms in hydrothermally altered rocks. Layer silicates partially transformed to clay minerals will be characterized using atomic-resolution transmission electron microscopy and state of the art energy-filtered electron microscopic techniques. Atomic-resolution and low dose image capture capabilities will be used to determine whether structural details of clay products are consistent with a transformation mechanism that involves structural inheritance. Our work will employ both weathered layer silicates from the rhizosphere region of natural soils and layer silicates weathered in a laboratory rhizosphere. The distribution of microorganisms on mineral surfaces will be studied using domain level and more specific oligonucleotide probes. The hypothesis that microorganisms in soils accelerate mineral dissolution by production of extracellular enzymes (e.g. "mineralases" , analogous to cellulases and chitinases microbes produce to degrade wood, chitin, and related organic substrates) will be tested. This work involves collaboration with Prof. Robert Goodman (Plant Pathology, UW-Madison.
