Role of protein nanowires in metal cycling and mineralization

蛋白质纳米线在金属循环和矿化中的作用

• 批准号: 1629439
• 负责人: Gemma Reguera
• 金额: $ 15.2万
• 依托单位: Michigan State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-09-01 至 2021-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1629439&HistoricalAwards=false
• 关键词: Role; protein; nanowires; metal; cycling

Geobacter bacteria are recognized as important agents in the cycling of iron and manganese. These bacteria "breath" iron and manganese oxides, a process that requires the cells to produce hair-like filaments (pili) to bind the minerals and discharge onto them electrons generated in their metabolism. The surface of these biological "nanowires" is decorated with pockets that could trap many other metals, particularly those that are positively charged (cationic metals). This suggests that the range of metals that Geobacter bacteria can cycle and mineralize is far greater than currently acknowledged. This project will investigate the metal spectrum that Geobacter cells can bind and mineralized with their conductive pili. This research will advance NSF's Mission "to promote the progress of science" by studying a novel form of microbial energy transduction that has global implications in nature. Not only are the metals targeted in these studies naturally abundant, they are also byproducts of many industrial activities and accumulate at toxic levels as highly mobile forms, which are rapidly introduced into the food chain and increase the risk of exposure. Investigating biological mechanisms for their immobilization will provide the fundamental knowledge needed to develop technologies for biomining and bioremediation, thus addressing a national need. The research is also intertwined with educational efforts directed at training young professionals at the interface of biology and geology, but with deep understanding of physics, chemistry, and engineering. Efforts are also aimed at training future educators and stirring their motivation to engage in outreach projects that promote science communication and inclusion.This project will focus on Geobacter bacteria, the only microorganisms described to date that use protein nanowires as electronic conduits between the cell and extracellular metal electron acceptors. Each pilus fiber is an assembly of the same peptide subunit (the pilin) and exposes on its surface many carboxyl side chain ligands, which could bind cationic metals and position them optimally for their reduction. The investigator will test this in a series of experiments that evaluate the effect of piliation, pilus conductivity, and charge of the putative metal traps to bind and reductively precipitate trivalent cobalt (Co3+), divalent cadmium (Cd2+) and monovalent silver (Ag+) metal cations. These cationic metals are found in environments where iron reduction by Geobacter spp. is an active process, a process mediated by protein nanowires, and mineralized concomitantly to the reduction of iron oxides. This suggests that the Geobacter pili also mediate the reductive precipitation of the soluble metal cations, which one can assess in biological assays coupled to microscopic examination of the cells and bulk X-ray Absorption Near Edge Structure (XANES) spectroscopic analyses. The researcher will also collect the LIII-edge extended X-ray absorption fine structure (EXAFS) spectra from the pili-associated mineral to model the atomic coordination about the metal. This will allow to characterize the mineral phase and identify the nanowire ligands that are responsible for metal mineralization.

固氮菌是铁、锰循环的重要媒介。这些细菌“呼吸”铁和锰的氧化物，这一过程需要细胞产生毛发状的细丝（皮利）来结合矿物质，并将新陈代谢中产生的电子释放到这些细丝上。这些生物“纳米线”的表面装饰有口袋，可以捕获许多其他金属，特别是那些带正电的金属（阳离子金属）。这表明，Geophysical细菌可以循环和矿化的金属范围远远大于目前所承认的。本计画将探讨锗细胞与其传导性皮利结合及矿化的金属光谱。这项研究将通过研究一种在自然界中具有全球影响的新型微生物能量转换形式，推进美国国家科学基金会“促进科学进步”的使命。这些研究中针对的金属不仅天然丰富，而且也是许多工业活动的副产品，并以高度移动的形式积累到有毒水平，迅速进入食物链并增加暴露风险。调查其固定的生物机制将提供开发生物采矿和生物补救技术所需的基本知识，从而满足国家的需要。该研究还与教育工作交织在一起，旨在培养生物学和地质学接口的年轻专业人员，但对物理，化学和工程有深刻的理解。该项目将重点关注Geelobacteria，这是迄今为止所描述的唯一一种使用蛋白质纳米线作为细胞和细胞外金属电子受体之间的电子导管的微生物。每个菌毛纤维是相同的肽亚基（菌毛蛋白）的组装体，并在其表面暴露许多羧基侧链配体，这些配体可以结合阳离子金属并将它们最佳定位以进行还原。研究者将在一系列实验中对此进行测试，这些实验评估了纤毛形成、纤毛导电性和推定的金属陷阱的电荷对结合和还原沉淀三价钴（Co3+）、二价镉（Cd2+）和单价银（Ag+）金属阳离子的影响。这些阳离子金属被发现在环境中，铁还原的Geodynamic spp。是一个活跃的过程，一个由蛋白质纳米线介导的过程，并伴随着铁氧化物的还原而矿化。这表明，锗皮利还介导可溶性金属阳离子的还原沉淀，这可以在生物测定中结合细胞的显微镜检查和本体X射线吸收近边结构（XANES）光谱分析来评估。研究人员还将收集来自pili相关矿物的LIII边扩展X射线吸收精细结构（EXAFS）光谱，以模拟金属的原子配位。这将允许表征矿物相并识别负责金属矿化的纳米线配体。