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

Lion/Ghiorse/Shuler摘要这项研究利用一个高度受控的实验室系统，确定了生物和化学对生物生成锰氧化物形成速度的耦合控制。实验系统以圆盘细毛藻为模型锰(II)氧化菌，梨形四膜虫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(铜和铅)的耦合命运进行机械解释，并开发适当的预测模型。这项研究采用了恒化型生物反应器系统，其中对物理条件(例如，雷诺数和水力停留时间)、化学条件(例如，介质成分、有毒金属形态、pH、O2水平)和生物特性(通过使用特定的培养物)保持控制。在受控的实验室条件下，人们正在研究一些可能影响Mn(II)氧化和金属生物积累的因素，包括：1)负责Mn(II)氧化的胞外酶的细菌产生速度，受营养浓度和形成活性酶所需的基本金属离子(例如，铜和可能的铁)浓度的限制；2)氧化锰涂层对捕食者细菌消耗的影响和被摄取的氧化锰的命运；3)锰氧化物结合的铅和胞外铜的生物积累/生物生长，与被认为是导致锰(II)氧化的多铜氧化酶有关，以及铜被吸附到通过酶活性形成的水合氧化锰上。

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.