Microbial Mediation of Manganese Cycling: Formation of Biogenic Mn Oxides, Oxide Scavenging of Toxic Metals, and Coupled Fates Subject to Predation by Protozoan Grazers

摘要本研究是利用高度控制的实验室系统确定生物源性锰氧化物形成速率的生物和化学耦合控制。该实验系统以钩螺旋体（Leptothrix discophora）为模型Mn（II）氧化细菌，梨形四膜虫（Tetrahymena pyriformis）为模型原生动物捕食者。实验控制包括使用可以确定金属形态的溶液，允许对添加到实验系统中的过渡金属（Cu和Pb）的耦合命运进行机制解释，并开发适当的预测模型。该研究采用了一种化学控制型生物反应器系统，在该系统中，对物理条件（如雷诺数和水力停留时间）、化学条件（如培养基成分、有毒金属形态、pH值、O2水平）和生物特性（通过使用定义的培养物）进行控制。受控的实验室条件有助于研究预计会影响锰（II）氧化和金属生物积累的若干因素，包括：1)受营养物浓度和形成活性酶所需的必需金属离子（例如Cu和可能的Fe）浓度的限制，负责锰（II）氧化的胞外酶的细菌生产速率；2)氧化锰涂层对捕食者细菌消耗的影响以及被摄入的氧化锰的命运；3)与多铜氧化酶有关的锰氧化物结合的铅和细胞外铜的生物积累/生物活化，多铜氧化酶被认为负责锰（II）氧化，以及通过酶的活性吸附到水合锰氧化物上的铜。

Lion/Ghiorse/Shuler AbstractThis 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.