EAGER: Assessment of Pseudo-nitzschia ferritin gene expression as a molecular indicator of iron nutritional status along natural iron gradients

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Iron availability limits productivity in 30-40% of the world's oceans. Microbes that persist in these regions must be able to rapidly take up and store iron when it is available and withstand long intervals of limited iron supply. Ferritins are highly specialized iron storage proteins present in many animals, plants and microorganisms. The investigators recently discovered that marine pennate diatoms possess ferritin and showed that iron availability was directly related to ferritin transcript abundance in both oceanic and coastal species of the cosmopolitan pennate diatom genus Pseudonitzschia. Whole genome sequence analysis indicated that ferritin is not present within the centric species, Thalassiosira pseudonana and the oceanic species P. granii underwent more cell divisions based on stored iron than an oceanic species of Thalassiosira. Based on these results, the investigators hypothesized that increased iron storage via ferritin provides a competitive advantage to pennate diatoms in low-iron environments that receive intermittent iron inputs and that the activity of ferritin underlies their dominance in oceanic iron fertilization experiments. This project relies on a combination of field and laboratory samples to test the hypothesis that transcript abundance of the ferritin gene (FTN) reflects the iron status of natural communities of the diatom Pseudonitzschia. First, they will utilize field samples collected from a natural iron gradien and from an iron grow-out microcosm experiment at a well-characterized iron-limited region, Ocean Station Papa. P. granii was abundant at all sampled sites, as well as in the iron-induced bloom and will serve as the target organism. Second, P. granii strains isolated from OSP will be investigated under controlled laboratory conditions to confirm that the transcript abundance of FTN is influenced by iron nutritional status and not other environmental parameters. This research is a good fit for support through the EAGER program as there is the potential for the development of a new molecular tool to elucidate the iron status of phytoplankton in the field but there is an urgent and limited time frame in which this research can be performed. The research will serve as a proof of principle study to verify the importance of pennate diatom ferritin and iron storage as a selective mechanism controlling the distributions of this ecologically important group.The outcome of the research will be development of a Pseudonitzschia Ferritin Index (PFI) that can be used by other research groups interested in assessing the iron nutritional status of natural mixed phytoplankton communities. Iron measurements are complicated by the diversity of compounds that complex iron present within field samples, potentially lowering the biological availability of iron. Development of the index will obviate these potential complications and would serve as a biologically relevant indicator of iron availability. Each year, six to seven undergraduates are given opportunities to conduct research in the Armbrust lab. Dr. Marchetti, an early career scientist, will continue to mentor an undergraduate to help with this project. All undergraduates have the opportunity to present their research at the Annual Undergraduate Research Symposium held each year at the University of Washington.