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/Shenyang摘要本研究使用高度受控的实验室系统确定生物和化学对生物锰氧化物形成速率的耦合控制。实验系统是以盘孢纤发菌为模式锰氧化菌，梨形四膜虫为模式原生动物捕食者。 实验控制包括使用的解决方案，其中金属形态可以确定，允许添加到实验系统和适当的预测模型的发展的过渡金属（铜和铅）的耦合命运的机械解释。该研究采用了恒化器型生物反应器系统，其中保持对物理条件的控制（例如，雷诺数和水力停留时间）、化学条件（例如，培养基组成、有毒金属形态、pH、O2水平）和生物学特性（通过使用确定的培养物）。受控的实验室条件有利于研究预期影响Mn（II）氧化和金属生物累积的许多因素，包括：1）细菌产生负责Mn（II）氧化的胞外酶的速率，其受到营养物浓度和必需金属离子浓度的限制（例如，2）锰氧化物涂层对捕食者细菌消耗的影响以及被摄入的锰氧化物的命运; 3）Mn（II）的生物富集/生物移动与多铜氧化酶有关的Mn氧化物结合的Pb和细胞外Cu氧化以及Cu吸附到通过酶的活性形成的水合Mn氧化物。

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.