Defining Critical Roles of Siderophore Structures in Environmental Trace Metal Cycling

该奖项是根据2009年《美国复苏和再投资法》(公法111-5)资助的。铁载体是生物体分泌的生物来源的螯合剂，通过络合增加铁的生物利用率，传统上排除了其他重要的痕量金属的参与，主要侧重于生物促进的铁的溶解和运输。最近的工作表明，铁载体可能参与生物溶解和吸收其他对环境重要的痕量金属，包括铬、锰和钴。铁载体可能对这些其他金属发挥重要的、可能是特定的作用，这是因为这些金属的铁载体络合物的稳定常数可能等于或超过铁的稳定常数。整个元素周期表中铁载体-金属结合强度的调色板，加上一些阳离子在氧化态之间穿梭的趋势，表明了一种丰富但在很大程度上未被探索的环境化学。尽管这些络合物在痕量金属循环中具有重要作用，因此也是土壤和天然水的初级生产力，但我们对它们的形成机制、控制溶液和矿物质-水界面稳定性的结构因素以及它们的环境反应性的认识仍存在重大差距。为了准确描述铁载体在金属生物地球化学中的复杂作用，需要对这些相互作用有更深入的了解。开创性的问题包括：铁载体和含铁载体的多配体混合物在从矿物中溶解痕量金属的效果如何？痕量金属-铁载体络合物在表面和环境相关的水条件下有多稳定？金属-铁载体络合物的反应能力如何与其他环境相关物种的生物地球化学循环相耦合？以及，金属-铁载体络合物的结构如何控制它们的金属选择性？这项研究项目将利用络合物形成-降解的方法来阐明金属-铁载体络合物的行为：通过铁载体促进金属(HIDR)氧化物的溶解形成络合物；表征水和吸附的金属-铁载体络合物的稳定性和结构；以及定量络合物与金属氧化物表面的反应活性，以及引起这种化学的分子尺度结构。现在越来越明显的是，铁载体参与了不同的环境化学，需要更复杂的范例来描述它们对铁以外痕量金属的生物地球化学循环的影响。拟议工作的学术价值源于开发了一种新的概念模型，以描述铁载体在环境中发挥的多方面作用。对这些过程的定量的分子尺度的理解将阐明铁载体影响痕量金属循环的基本机制，并通过生物地球化学和地球生物学在这些金属和其他元素之间建立联系。拟议工作的更广泛影响从地球科学的基本发现延伸到教育、广泛的跨学科科学领域和环境管理。该项目将为一名职业生涯早期的科学家提供经验，并为一名NCSU研究生和一组布鲁克林学院本科生提供广泛的、多学科的教育。达克沃斯帮助在地区大学开展了一系列访问研讨会，以招收研究生，特别是来自代表性不足群体的研究生。布鲁克林学院在培养不同学生的学术和研究方面有着良好的记录。此外，NCSU将为地区高中教师提供为期两天的研讨会。今年暑期的外展活动将与科学之家联合开展，科学之家是一个组织，其使命是与K-12教师合作，增加在数学和科学领域中实践学习技术的使用和影响。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The perceived environmental roles of siderophores, biogenic chelating agents exuded by organisms to increase the bioavailability of iron by complexation, have traditionally excluded the involvement of other important trace metals and focused largely on biologically facilitated iron solubilization and transport. Recent work has suggested that siderophores likely are involved in the biological solubilization and uptake of other environmentally important trace metals, including Cr, Mn, and Co. That siderophores may play important, possibly specific, roles with these other metals is suggested by the fact that siderophore complexes of these metals may have stability constants that equal or exceed those for ferric iron. The palette of siderophore-metal binding strengths that occurs across the periodic table, combined with the tendency for some cations to shuttle between oxidation states, suggests a rich but largely unexplored environmental chemistry. In spite of the imputed importance of these complexes in trace metal cycling and hence the primary productivity of soils and natural waters, significant gaps exist in our knowledge of their formation mechanisms, the structural factors that govern stability in solution and at mineral-water interfaces, and their environmental reactivity. A deeper understanding of these interactions is required to accurately describe the complicated role of siderophores in metal biogeochemistry. Seminal questions include: How effective are siderophores and siderophore-containing multi-ligand mixtures at solubilizing trace metals from minerals?; How stable are trace metal-siderophore complexes at surfaces and under environmentally relevant aqueous conditions?; How does the reactivity of metal-siderophore complexes couple to the biogeochemical cycling of other environmentally relevant species?; And, how do the structures of metal-siderophore complexes control their metal selectivity? This research project will utilize a complex formation-to-degradation approach to elucidate metal-siderophore complex behavior: formation of complexes by siderophore-promoted dissolution of metal (hydr)oxides; characterization of the stability and structure of aqueous and adsorbed metal-siderophore complexes; and quantitation of the reactivity of complexes with metal oxide surfaces, and the molecular-scale structures that give rise to this chemistry. It is now becoming apparent that siderophores engage in a diverse environmental chemistry, and that more complex paradigms are required to describe their effects on the biogeochemical cycling of trace metals beyond iron. The intellectual merit of the proposed work stems from the development of a new conceptual model to describe the multifaceted roles played by siderophores in the environment. A quantitative molecular-scale understanding of these processes will elucidate fundamental mechanisms by which siderophores affect the cycling of trace metals and forge linkages between these metals and other elements through biogeochemistry and geobiology. The broader impacts of the proposed work reach beyond basic discovery in the earth sciences to education, broad interdisciplinary scientific realms, and environmental management. The project will provide experience to an early-career scientist as well as a broad, multidisciplinary education to an NCSU graduate student and a team of Brooklyn College undergraduates. Duckworth helps to spearhead a series of visiting seminars at area colleges to recruit graduate students, especially from underrepresented groups. Brooklyn College has a strong track record of training diverse students in both academics and research. In addition, NCSU will offer a two-day workshop for area high-school teachers. This summer outreach activity will be conducted in conjunction with the Science House, an organization whose mission is to work in partnership with K-12 teachers to increase the use and impact of hands-on learning technologies in the fields of math and science.