2010 Annual Science Report
Arizona State University Reporting | SEP 2009 – AUG 2010
Stoichiometry of Life - Task 1e- Experimental Studies - Diatom Growth on Iron Nanoparticles
In some environments (such as ocean regions fed by icebergs), the critical element iron (Fe) is supplied in the form of very small (“nano”) particles that are suspended rather than dissolved in water. However, it’s not known if this nanoparticle Fe is available to microscopic phytoplankton. This project involves experiments testing whether diatoms (a key oceanic phytoplankton group) can access nanoparticle Fe.
In collaboration with Emeritus Professor Robert Raiswell of University of Leeds, a group of ASU graduate students (Jen Glass, G. Alex Hamilton, Katie Alexander, Rebecca Mestek, Jennifer Morgan, Jessie Shipp) from the laboratory groups of Hilairy Hartnett, Susanne Neuer and Ariel Anbar performed experiments to investigate the bioavailabilty of iron ferrihydrite nanoparticles to the growth of polar diatoms. Antarctic icebergs are a potential source of Fe to the Southern Ocean, where primary productivity is Fe-limited. Iceberg-hosted sediments contain nanoparticulate Fe oxyhydroxides, of which ferrihydrite is potentially most bioavailable. To investigate the bioavailability of nanoparticulate ferrihydrite, the Arctic pennate diatom Entomoneis sp. CCMP 2396 was grown in artificial seawater containing either synthesized 2-line ferrihydrite (as aggregates of nanoparticles ~ 5 nm diameter), ferric sulfate or no added Fe. Growth rates for the treatment with ferrihydrite nanoparticles were significantly higher than the other two growth conditions. Furthermore, extremely high concentrations of Fe (>2700 ppm) were associated with cells incubated with nanoparticles, suggesting that nanoparticles interact with the cell surface and provide Fe to the cells. These results suggest that nanoparticle Fe is bioavailable and does not require ligand-aided dissolution before uptake. In addition, our findings support the hypothesis that nanoparticulate iceberg Fe fertilizes oceanic productivity in the Southern Ocean today, and may have significantly increased productivity throughout the ocean during the Last Glacial Maximum.
PROJECT INVESTIGATORS:Jennifer Glass
PROJECT MEMBERS:James Elser
RELATED OBJECTIVES:Objective 6.1
Effects of environmental changes on microbial ecosystems