Lion/Ghiorse/Shuler Abstract This research is determining the coupled biological and chemical controls on the rate of formation of biogenic Mn oxides using a highly controlled laboratory system. The experimental system is using Leptothrix discophora as a model Mn(II)-oxidizing bacterium and Tetrahymena pyriformis as a model protozoan predator. Experimental control include the use of solutions in which metal speciation can be determined, permitting a mechanistic interpretation of the coupled fate of transition metals (Cu and Pb) added to the experimental system and development of appropriate predictive models. The research is employing a chemostat-type bioreactor system in which control is maintained over physical conditions (e.g., Reynolds number, and hydraulic retention time), chemical conditions (e.g., medium composition, toxic metal speciation, pH, O2 level) and biological properties (via use of defined cultures). The controlled laboratory conditions is facilitating the investigation of a number of factors that are expected to influence Mn(II) oxidation and metal bioaccumulation, including: 1) the rate of bacterial production of the extracellular enzymes responsible for Mn(II) oxidation subject to the constraints of nutrient concentrations and the concentration of essential metal ions (e.g., Cu and possibly Fe) that may be required for formation of active enzymes; 2) the influence of Mn oxide coatings on bacterial consumption by predators and the fate of Mn oxides that are ingested; 3) the bioaccumulation/ biomobilization ofMn oxide-bound Pb and extracellular Cu associated with the multicopper oxidase enzymes thought to be responsible for Mn(II) oxidation as well as the Cu adsorbed to the hydrous Mn oxides formed through the activity of the enzyme.
