Nitrogenase metal cofactors in terrestrial systems: Chemical speciation and the kinetic versus thermodynamic controls on metal acquisition by diazotrophs using metallophores

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Dr. Frank J. Black has been granted the NSF Earth Sciences Postdoctoral Fellowship to carry out a research and education plan at Princeton University. The research will contribute to the understanding of how the amount and forms of trace metals (Mo and V) in soils and leaf litter influence the activity of free living nitrogen fixing bacteria, and how these bacteria tailor their strategies for metal acquisition to adapt to different soil environments. The research to be conducted aims to understand (1) what forms of vanadium and molybdenum are found in soils and leaf litter where nitrogen fixation occurs, (2) how available these different forms are to nitrogen fixing bacteria, and (3) which mechanisms developed by bacteria to acquire these metals are more effective under different soil conditions. Bacteria have developed various approaches to acquiring iron in soils even from normally unavailable forms, and this research will test how effective bacteria are at acquiring molybdenum and vanadium under similar conditions. Plant growth and CO2 utilization in many ecosystems is limited by the availability of the nutrient nitrogen. Some soil bacteria are able to fix nitrogen from the atmosphere and make it bioavailable, but in order to do so they require a combination of the metals molybdenum, vanadium, and iron. These metals are often in short supply in soils (e.g., molybdenum), or are bound in forms not readily accessible to bacteria (e.g., iron). The low availability of these metals in soil environments is a potentially important control on nitrogen fixation, and in turn on the productivity of entire ecosystems. Teaching and educational outreach activities associated with the project will include helping to design and teach the laboratory section of a freshman seminar course using inquiry based techniques.