Molecular Mechanisms of Soluble Fe(III) Reduction by Metal-Reducing Members of the Genus Shewanella

铁是地壳中第四丰富的元素，在许多元素的地球化学循环中起着至关重要的作用。然而，对厌氧系统中微生物介导的Fe（III）还原知之甚少。 此类反应涉及多种对环境具有重要意义的过程，包括Fe、Mn、微量元素和磷酸盐的生物地球化学循环;有机物的降解;含Fe（III）的粘土和矿物的风化;以及生物矿化含Fe（II）的矿物，例如磁铁矿。 这项工作将由格鲁吉亚理工学院的研究人员进行，旨在确定希瓦氏菌属金属还原成员溶解并随后还原可溶性Fe（III）的分子机制。互补的遗传，生物化学和原位伏安法将被用来克隆希瓦氏菌基因参与溶解和随后的可溶性铁（III）的减少。从这些基因表达的可溶性Fe（III）还原酶将通过原位伏安法分析蛋白质结构特征和电子供体氧化和电子受体还原活性。纯化的还原酶也将用作抗原以产生可溶性Fe（III）还原酶抗体，用于确定还原酶在希瓦氏菌中的亚细胞位置。 自然环境中的可溶性Fe（III）可能来源于Fe（III）还原菌，其合成并分泌Fe（III）增溶化合物。 这项工作将提供第一个证据表明，Fe（III）还原细菌在可溶性Fe（III）的生产中发挥重要作用。从我们提出的研究结果也将证明固体Fe（III）的增溶铁（III）还原细菌在铁循环的重要性。由于Fe（III）的生物利用度取决于固体Fe（III）的结晶度、外源螯合剂的可用性或固体Fe（III）上活性位点的丰度，因此Fe（III）还原细菌可能通过使用多种Fe（III）还原途径来适应其环境条件。 拟议中的研究将提供新的信息的基因和预测的基因产物所需的合成和分泌内源性Fe（III）增溶化合物和Fe（III）还原酶。这些信息将用于后续研究，以确定增溶化合物的化学组成，并将通过关注研究不足的途径来深入了解这种可能性。从我们的研究结果将有助于完善成岩模型，其中Fe（III）被认为是一个反应性固体，因此可能有显着的影响，地球化学领域。就更广泛的教育影响而言，这项研究将吸引来自两个不同但互补的学科的学生，他们将联合收割机结合自己的专业知识来解决复杂的地球化学问题。

Iron is the fourth most abundant element in the Earth's crust and plays an essential role in the biogeochemical cycling of many elements. Yet little is known about microbially mediated Fe(III) reduction in anaerobic systems. Such reactions are to a wide variety of environmentally significant processes, including the biogeochemical cycling of Fe, Mn, trace elements, and phosphate; degradation of organic matter; weathering of Fe(III)-containing clays and minerals; and biomineralization of Fe(II)-bearing minerals such as magnetite. This work, which will be carried out by researchers at the Georgia Institute of Technology, strives to determine the molecular mechanism by which metal-reducing members of the genus Shewanella solubilize and subsequently reduce soluble Fe(III). Complementary genetic, biochemical, and in situ voltammetric approaches will be used to clone the Shewanella genes involved in solubilization and subsequent reduction of soluble Fe(III). The soluble Fe(III) reductases expressed from these genes will be analyzed for protein structural characteristics and electron donor oxidation and electron acceptor reduction activities via in situ voltammetry. The purified reductases will also be used as the antigen to generate soluble Fe(III) reductase antibodies for determining the subcellular location of the reductases in Shewanella. Soluble Fe(III) in natural environments may originate from Fe(III)-reducing bacteria which synthesize and excrete Fe(III)-solubilizing compounds. This work will provide the first evidence that Fe(III)-reducing bacteria play a significant role in the production of soluble Fe(III). Results from our proposed study will also demonstrate the importance of the solubilization of solid Fe(III) by Fe(III)-reducing bacteria in iron cycling. Because the bioavailability of Fe(III) depends on the crystallinity of solid Fe(III), the availability of exogenous chelators, or the abundance of active sites onto solid Fe(III), it is possible that Fe(III)-reducing bacteria adapt to their environmental conditions by using multiple Fe(III) reduction pathways. The proposed research will provide novel information on the genes and predicted gene products required to synthesize and excrete endogenous Fe(III)-solubilizing compounds and Fe(III) reductases. This information will be used in subsequent studies to determine the chemical composition of the solubilizing compounds and will provide insights into this possibility by focusing on a poorly studied pathway. Results from our study will help refine diagenetic models in which Fe(III) is assumed to be a reactive solid and may therefore have a significant impact on the fields of biogeochemistry. In terms of broader educational impacts, this study will engage students from two disparate, yet complementary disciplines who will combine their expertise to tackle a complex biogeochemical problem.