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

铁是地壳中含量第四丰富的元素，在许多元素的生物地球化学循环中起着至关重要的作用。然而，对于厌氧系统中微生物介导的铁（III）还原知之甚少。这些反应涉及各种各样的环境重要过程，包括铁、锰、微量元素和磷酸盐的生物地球化学循环；有机物降解；含铁（III）粘土和矿物的风化作用；以及磁铁矿等含铁矿物的生物矿化作用。这项工作将由佐治亚理工学院的研究人员进行，致力于确定希瓦氏菌属金属还原成员溶解并随后还原可溶性铁（III）的分子机制。互补的遗传、生化和原位伏安方法将用于克隆参与可溶性铁的溶解和随后还原的希瓦氏菌基因（III）。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，产生可溶性铁（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铁（III）可能来源于铁（III）还原菌，它们合成并排泄铁（III）溶解性化合物。这项工作将提供第一个证据，证明铁（III）还原细菌在可溶性铁（III）的生产中发挥重要作用。我们提出的研究结果也将证明铁（III）还原细菌对固体铁（III）的增溶作用在铁循环中的重要性。由于铁（III）的生物利用度取决于固体铁（III）的结晶度、外源螯合剂的可用性或固体铁（III）上活性位点的丰度，因此铁（III）还原细菌有可能通过多种铁（III）还原途径来适应其环境条件。拟议的研究将为合成和排泄内源性铁（III）溶解化合物和铁（III）还原酶所需的基因和预测基因产物提供新的信息。这些信息将用于后续的研究，以确定增溶化合物的化学成分，并将通过关注研究较少的途径来深入了解这种可能性。我们的研究结果将有助于完善成岩模型，其中Fe（III）被认为是一种活性固体，因此可能对生物地球化学领域产生重大影响。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，他们将结合他们的专业知识来解决复杂的生物地球化学问题。

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.