title: Development of a molecular-based index for assessing iron status in bloom-forming pennate diatoms.
abstract: Iron availability limits primary productivity in large areas of the world's oceans. Ascertaining the iron status of phytoplankton is essential for understanding the factors regulating their growth and ecology. We developed an incubation-independent, molecular-based approach to assess the iron nutritional status of specific members of the diatom community, initially focusing on the ecologically important pennate diatom Pseudo-nitzschia. Through a comparative transcriptomic approach, we identified two genes that track the iron status of Pseudo-nitzschia with high fidelity. The first gene, ferritin (FTN), encodes for the highly specialized iron storage protein induced under iron-replete conditions. The second gene, ISIP2a, encodes an iron-concentrating protein induced under iron-limiting conditions. In the oceanic diatom Pseudo-nitzschia granii (Hasle) Hasle, transcript abundance of these genes directly relates to changes in iron availability, with increased FTN transcript abundance under iron-replete conditions and increased ISIP2a transcript abundance under iron-limiting conditions. The resulting ISIP2a:FTN transcript ratio reflects the iron status of cells, where a high ratio indicates iron limitation. Field samples collected from iron grow-out microcosm experiments conducted in low iron waters of the Gulf of Alaska and variable iron waters in the California upwelling zone verify the validity of our proposed Pseudo-nitzschia Iron Limitation Index, which can be used to ascertain in situ iron status and further developed for other ecologically important diatoms.
authors.affiliation: Department of Marine Sciences, University of North Carolina at Chapel Hill, CB 3300, Chapel Hill, North Carolina, 27599, USA.
authors.forename: Adrian
authors.identifier: 0000-0003-4608-4775
authors.initials: A
authors.lastname: Marchetti
authors.affiliation: Department of Marine Sciences, University of North Carolina at Chapel Hill, CB 3300, Chapel Hill, North Carolina, 27599, USA.
authors.forename: Carly M
authors.initials: CM
authors.lastname: Moreno
authors.affiliation: Department of Marine Sciences, University of North Carolina at Chapel Hill, CB 3300, Chapel Hill, North Carolina, 27599, USA.
authors.forename: Natalie R
authors.initials: NR
authors.lastname: Cohen
authors.affiliation: Department of Biomedical Science, Florida Atlantic University, 777 Glades Road, BC-71, Boca Raton, Florida, 33431, USA.
authors.forename: Irina
authors.initials: I
authors.lastname: Oleinikov
authors.affiliation: Department of Marine Sciences, University of North Carolina at Chapel Hill, CB 3300, Chapel Hill, North Carolina, 27599, USA.
authors.forename: Kimberly
authors.initials: K
authors.lastname: deLong
authors.affiliation: Bigelow Laboratory for Ocean Sciences, 60 Bigelow Dr., PO Box 380, East Boothbay, Maine, 04544, USA.
authors.forename: Benjamin S
authors.initials: BS
authors.lastname: Twining
authors.affiliation: School of Oceanography, University of Washington, Benjamin Hall IRB, 616 NE Northlake Place, Seattle, Washington, 98105, USA.
authors.forename: E Virginia
authors.initials: EV
authors.lastname: Armbrust
authors.affiliation: Department of Marine Sciences, University of North Carolina at Chapel Hill, CB 3300, Chapel Hill, North Carolina, 27599, USA.
authors.forename: Robert H
authors.initials: RH
authors.lastname: Lampe
mesh_terms: D020418:Algal Proteins / Q000235:genetics* / Q000378:metabolism; D017377:Diatoms / Q000235:genetics* / Q000378:metabolism*; D005293:Ferritins / Q000235:genetics* / Q000378:metabolism; D020869:Gene Expression Profiling; D007501:Iron / Q000378:metabolism*; D010839:Phytoplankton / Q000235:genetics / Q000378:metabolism
chemical_list: D020418:Algal Proteins; D005293:Ferritins; D007501:Iron
keywords: 
  Pseudo-nitzschia
  ; diatoms; gene expression; iron status; molecular indicator