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Regulation of the phytoplankton heme b iron pool during the North Atlantic spring bloom

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Louropoulou, E, Gledhill, M, Browning, TJ, Desai, DK, Menzel Barraqueta, J-L, Tonnard, M, Sarthou, G, Planquette, H, Bowie, AR ORCID: 0000-0002-5144-7799, Schmitz, RA, LaRouche, J and Achterberg, EP 2019 , 'Regulation of the phytoplankton heme b iron pool during the North Atlantic spring bloom' , Frontiers in Microbiology, vol. 10 , pp. 1-16 , doi: 10.3389/fmicb.2019.01566.

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Abstract

Heme b is an iron-containing co-factor in hemoproteins. Heme b concentrations are low (-1) in iron limited phytoplankton in cultures and in the field. Here, we determined heme b in marine particulate material (>0.7 μm) from the North Atlantic Ocean (GEOVIDE cruise – GEOTRACES section GA01), which spanned several biogeochemical regimes. We examined the relationship between heme b abundance and the microbial community composition, and its utility for mapping iron limited phytoplankton. Heme b concentrations ranged from 0.16 to 5.1 pmol L-1 (median = 2.0 pmol L-1, n = 62) in the surface mixed layer (SML) along the cruise track, driven mainly by variability in biomass. However, in the Irminger Basin, the lowest heme b levels (SML: median = 0.53 pmol L-1, n = 12) were observed, whilst the biomass was highest (particulate organic carbon, median = 14.2 μmol L-1, n = 25; chlorophyll a: median = 2.0 nmol L-1, n = 23) pointing to regulatory mechanisms of the heme b pool for growth conservation. Dissolved iron (DFe) was not depleted (SML: median = 0.38 nmol L-1, n = 11) in the Irminger Basin, but large diatoms (Rhizosolenia sp.) dominated. Hence, heme b depletion and regulation is likely to occur during bloom progression when phytoplankton class-dependent absolute iron requirements exceed the available ambient concentration of DFe. Furthermore, high heme b concentrations found in the Iceland Basin and Labrador Sea (median = 3.4 pmol L-1, n = 20), despite having similar DFe concentrations to the Irminger Basin, were attributed to an earlier growth phase of the extant phytoplankton populations. Thus, heme b provides a snapshot of the cellular activity in situ and could both be used as indicator of iron limitation and contribute to understanding phytoplankton adaptation mechanisms to changing iron supplies.

Item Type: Article
Authors/Creators:Louropoulou, E and Gledhill, M and Browning, TJ and Desai, DK and Menzel Barraqueta, J-L and Tonnard, M and Sarthou, G and Planquette, H and Bowie, AR and Schmitz, RA and LaRouche, J and Achterberg, EP
Keywords: phytoplankton, heme b, iron, North Atlantic, spring bloom
Journal or Publication Title: Frontiers in Microbiology
Publisher: Frontiers Research Foundation
ISSN: 1664-302X
DOI / ID Number: 10.3389/fmicb.2019.01566
Copyright Information:

Copyright 2019 Louropoulou, Gledhill, Browning, Desai, Menzel Barraqueta, Tonnard, Sarthou, Planquette, Bowie, Schmitz, LaRoche and Achterberg. Licensed under Creative Commons Attribution 4.0 International (CC BY 4.0) https://creativecommons.org/licenses/by/4.0/

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