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.

National Science Foundation (NSF)
Division of Earth Sciences (EAR)
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Enriqueta Barrera
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North Carolina State University Raleigh
United States
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