Copper and iron limitation and interaction in marine diatoms

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Surface waters of the open sea contain some of the lowest concentrations of dissolved metals of any environment. Most of the metals are essential for plankton, as co-factors of enzymes and redox proteins involved in cellular metabolism. They catalyze reactions and chemical transformations that are critical parts of all of the major biogeochemical cycles on Earth. Iron (Fe), one of the least soluble metals in seawater, is a limiting resource for phytoplankton in the contemporary ocean. Its low concentration restricts carbon (C) production, influences community structure and function, and affects the cycling of other metals and macronutrients. Discovering the processes that influence Fe availability and utilization are key to understanding the ecology of the Fe-limited sea. This knowledge will inform us of how the ocean functions biologically and how it may respond to change in the future. The objectives of the research are: 1) to study how autotrophic and heterotrophic plankton acquire trace metals and adapt and acclimate when they are limiting, 2) to determine the dominant roles that these metals play in cellular metabolism, and 3) to identify the symptoms and consequences (ecological and biogeochemical) of metal limitation in the sea. This proposal addresses three important topics that relate to the objectives: 1) How widespread is Cu substitution for Fe in oceanic diatoms?, 2) How prevalent is Cu limitation in the sea and how does it affect Cu and Fe uptake by phytoplankton?, and 3) How does Fe-limitation affect the requirements of phytoplankton for other metals and their abilities to tolerate oxidative stress? The work will contribute to our understanding of how Fe regulates plankton production in the sea and the ways in which organisms adapt and compete for this limiting resource.