Collaborative Research: Oxygen Isotope Tracers of Bacterial Manganese Oxidation

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The reactions leading to the formation of geological metal ore deposits are complex, and the potential role of microorganisms in the formation of some low-temperature ore deposits, while recognized, has not been fully assessed. In the past 9 months the investigators developed techniques for measuring the 18O of manganese oxides and are using these measurements to compare microbial and nonbiological manganese oxidation mechanisms. They hypothesize that measurements of the oxygen isotopic composition of Mn oxides can be used as geologic tracers for the microbial origin of Mn deposits or as a paleoindicator of the dissolved oxygen content, and there fore Eh conditions, of the water from which the deposit was formed. Progress has been made in establishing the technical feasibility of this approach. They will continue using oxygen isotopes to examine mechanisms of chemical and biological Mn(II) oxidation and determine if the isotopic signature of Mn oxides persist under environmental conditions. First, they will assess the stability of the oxygen tracer in the manganese oxide by a series of exchange experiments with different Mn oxide minerals precipitated biologically and chemically. Second, they will determine if bacteria fractionate oxygen isotopes during Mn(II) oxidation by measuring the 18O of the initial and residual reactant (O2) as well as the Mn oxide product. Third, the diversity of microbial mechanisms will be investigated by culturing a variety of Mn(ii) oxidizing bacteria and measuring the 18O of their oxides. Last, the relationship between dissolved oxygen concentration and the 18O of the manganese oxides will be tested in the field in anoxic water columns beginning with initial studies in the Black Sea and culminating in two cruises to an anoxic marine fjord. This research has significant implications for paleoenvironmental studies.