Molecular Environmental Chemistry of Mn Oxide Biomineralization

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This Collaborative Research Activities in Environmental Molecular Science (CRAEMS) Award to the University of California-San Diego Scripps Institute of Oceanography is supported by the Special Projects Office in the Chemistry Division. In addition to the support to Bradley Tebo at the Institute, the award also supports Thomas Spiro at Princeton University, John Bargar at the Stanford Synchrotron Radiation Laboratory and Garrison Sposito at UC-Berkeley, through subawards. The award will address the issues of how bacteria oxidize manganese, how the resulting manganese oxides influence the chemistry of other metals in both terrestrial and marine environments and how they affect chemical and biochemical degradation of natural and xenobiotic organic molecules. The project will encompass (1) cloning and expressing the gene products associated with the Mn (II)-oxidation system of bacteria and characterizing these proteins using biochemical and spectroscopic methods in order to elucidate the mechanisms of manganese oxide formation; (2) investigating cross-reactivity with other metal ions and with organic molecules, in order to evaluate the environmental influence of Mn (II) oxidation systems; (3) exploring how metal ion co-contaminants are sequestered during manganese oxide biogenesis by whole cells; and (4) characterizing the reactivity of biogenic manganese oxide surfaces with respect to metal ion sorption and dissolution, and the alteration of organic substrates for microbial metabolism. A variety of microbiological, chemical, and spectroscopic techniques such as x-ray absorption spectroscopy, resonance Raman and FTIR will be utilized. Microbially produced manganese oxides are ubiquitous in the environment and have high capacities to transform organic and inorganic pollutants including aromatic hydrocarbons and hydrogen sulfide. Understanding the steps along the environmental trajectory of manganese oxides, from biochemical mechanisms, to cross-reactivity with metals and organics, to the influence of the oxides on metals immobilization and on biodegradation pathways, will be useful in elucidating biogeochemical cycles and designing remediation strategies for metal and organic pollution.