UC San Diego

This research characterized the Mn(II) oxidizing bacterial populations in a freshwater creek and a stratified marine basin, determined their response to O₂ concentrations and examined mechanisms that produce oxidized Mn in situ. As introduced in Chapter I, biogenic Mn oxides are reactive, ubiquitous minerals that adsorb and/or oxidize metals, inorganics and organics, thereby influencing the surrounding chemistry. Chapter II describes a diverse group of Mn(II) oxidizing bacteria from Pinal Creek, an Arizona stream impacted by mine pollution that is naturally attenuated by biogenic Mn oxides. In mixed Pinal Creek cultures, biogenic Mn oxides were produced preferentially at low O₂ concentration in close association with Mn oxide reducing organisms. Chapter III details the low O₂ concentrations required for biologic Mn(II) oxidation in the Black Sea, a stratified marine basin where Mn oxides play a large role in chemical interactions. Mn oxide production was observed at O₂ concentrations below the typical detection limits of 3-5 [mu]M, at rates more rapid than predicted by biogeochemical models. Chapter IV reports cultivation- independent confirmation that Mn(II)-oxidizing Pseudoalteromonas spp. isolated from the Black Sea can be abundant within the Mn oxide rich layer. These organisms both oxidize Mn(II) and produce the Mn(III)-binding siderophore desferrioxamine E. Chapter V illustrates that current knowledge about dissolved, oxidized Mn in natural systems is incomplete and describes an assay for Mn(III)- complex production that, when applied in the Black Sea indicated that direct and indirect mechanisms for oxidizing Mn(II) may co-occur. Finally, Chapter VI details open questions in and novel opportunities for bacterial Mn(II) oxidation research