Respiration-linked Metal Reduction in Bacteria

最近才分离出能够将其厌氧生长与锰(IV)和铁(III)还原相结合的微生物，使研究将锰(IV)和铁(III)用作厌氧呼吸的末端电子受体的微生物过程的生理和生化成为可能。这些微生物可能是这些金属在水和土壤环境中循环的重要生物地球化学因素。该项目更直接的目标包括研究这样一种微生物--腐生希瓦氏菌(原Alteromonas)菌株MR-1，包括：(1)测定当生长与锰或铁的还原相结合时的生长能量学，并将这些能量学与使用其他电子受体(O2、硝酸盐和富马酸)的生长能量学进行比较；(2)这些金属呼吸还原所涉及的电子传递组分的测定和初步表征；以及(3)负责这些金属还原的末端还原酶的提纯和表征。这项工作的几个方面构成了其科学原理的基础。首先，某些细菌将其生长与锰和铁氧化物的溶解结合起来的能力代表了一种新的细菌新陈代谢形式；这个项目揭示了迄今为止未知的细菌生理和生化方面。对这些机制的深入了解拓宽了关于无氧(即无氧)呼吸的知识现状，目前这些知识仅限于对少数细菌的研究。这种多样性使这种细菌成为研究无氧呼吸的组成和调节的有价值的模型。第三，由于这种细菌可以对水中沉积物和淹水土壤中的锰和铁的循环做出重大贡献，对其金属还原机理的了解有助于我们理解金属还原细菌在环境中的作用。总体而言，这些研究带来了关于无氧呼吸以及某些金属的环境循环的新思路。

Microbes that can couple their anaerobic growth to the reduction of manganese(IV) and iron(III) have only recently been isolated and make it possible to investigate the physiology and biochemistry of the microbial processes responsible for the use of manganese(IV) and iron(III) as terminal electron acceptor for anaerobic respiration. These microbes may act as important biogeochemical agents for the cycling of these metals in aquatic and soil environments. The more immediate objectives of this project include the study of one such microbe, Shewanella (formerly Alteromonas) putrefaciens strain MR-1, including: (1) determination of the growth energetics when growth is coupled to the reduction of manganese or iron, and comparison of these energetics to those involving the use of other electron acceptors(O2, nitrate, and fumarate); (2) determination and preliminary characterization of the electron transport components involved in the respiratory reduction of these metals; and (3) purification and characterization the terminal reductases responsible for the reduction of these metals. Several aspects of this work form the foundation for its scientific rationale. First, the ability of certain bacteria to couple their growth to the dissolution of manganese and iron oxides represents a novel form of bacterial metabolism; this project uncovers aspects of bacterial physiology and biochemistry heretofore unknown. Gaining insight into these mechanisms broadens the current state of knowledge concerning anaerobic (i.e. oxygen-free) respiration, knowledge which is currently limited to studies of only a few bacteria. Such versatility makes this bacterium a valuable model for studying the components and regulation of oxygen-free respiration. Thirdly, as this bacterium could make a significant contribution to the cycling of manganese and iron in aquatic sediments and flooded soils, knowledge of its mechanisms of metal reduction enhances our understanding of the roles of metal-reducing bacteria in the environment. Overall, the studies lead to new ways of thinking about oxygen-free respiration, as well as the environmental cycling of certain metals.