Role of protein nanowires in metal cycling and mineralization

地杆菌被认为是铁和锰循环的重要媒介。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（菌毛）来结合矿物质，并将代谢过程中产生的电子释放到它们身上。这些生物“纳米线”的表面装饰着可以捕获许多其他金属的口袋，特别是那些带正电的金属（阳离子金属）。这表明地杆菌细菌可以循环和矿化的金属的范围远远大于目前所承认的。这个项目将研究地杆菌细胞可以结合和矿化的金属光谱。这项研究将通过研究一种具有全球意义的微生物能量转导的新形式，推进美国国家科学基金会“促进科学进步”的使命。这些研究的目标金属不仅天然丰富，而且它们也是许多工业活动的副产品，并以高度流动的形式积累到有毒水平，迅速进入食物链，增加了暴露的风险。研究其固定的生物学机制将为开发生物矿化和生物修复技术提供所需的基础知识，从而解决国家需求。这项研究还与教育工作交织在一起，旨在培养生物学和地质学领域的年轻专业人员，同时对物理学、化学和工程学有着深刻的理解。这些努力还旨在培训未来的教育工作者，并激发他们参与促进科学传播和包容的外联项目的动机。该项目将重点研究地杆菌，这是迄今为止描述的唯一一种利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通道的微生物。每根毛纤维都是同一肽亚基（毛蛋白）的一个组装体，并在其表面暴露出许多羧基侧链配体，这些配体可以结合阳离子金属并使其处于还原的最佳位置。研究者将通过一系列的实验来验证这一点，这些实验将评估粘附、毛丝电导率和假定的金属陷阱的电荷对三价钴（Co3+）、二价镉（Cd2+）和一价银（Ag+）金属阳离子的结合和还原沉淀的影响。这些阳离子金属是在地杆菌对铁的还原是一个活跃过程的环境中发现的，这个过程是由蛋白质纳米线介导的，并且与氧化铁的还原同时矿化。这表明毛杆菌也介导可溶性金属阳离子的还原沉淀，这可以通过结合细胞显微镜检查和体x射线吸收近边缘结构（XANES）光谱分析的生物分析来评估。研究人员还将从与毛相关的矿物中收集liii边缘扩展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，并确定负责金属矿化的纳米线配体。

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.