AUTHOR=Louropoulou Evangelia , Gledhill Martha , Browning Thomas J. , Desai Dhwani K. , Barraqueta Jan-Lukas Menzel , Tonnard Manon , Sarthou Géraldine , Planquette Hélène , Bowie Andrew R. , Schmitz Ruth A. , LaRoche Julie , Achterberg Eric P. 

TITLE=Regulation of the Phytoplankton Heme b Iron Pool During the North Atlantic Spring Bloom

JOURNAL=Frontiers in Microbiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2019.01566

DOI=10.3389/fmicb.2019.01566

ISSN=1664-302X

ABSTRACT=<p>Heme <italic>b</italic> is an iron-containing co-factor in hemoproteins. Heme <italic>b</italic> concentrations are low (&lt;1 pmol L<sup>-1</sup>) in iron limited phytoplankton in cultures and in the field. Here, we determined heme <italic>b</italic> in marine particulate material (&gt;0.7 μm) from the North Atlantic Ocean (GEOVIDE cruise – GEOTRACES section GA01), which spanned several biogeochemical regimes. We examined the relationship between heme <italic>b</italic> abundance and the microbial community composition, and its utility for mapping iron limited phytoplankton. Heme <italic>b</italic> concentrations ranged from 0.16 to 5.1 pmol L<sup>-1</sup> (median = 2.0 pmol L<sup>-1</sup>, <italic>n</italic> = 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 <italic>b</italic> levels (SML: median = 0.53 pmol L<sup>-1</sup>, <italic>n</italic> = 12) were observed, whilst the biomass was highest (particulate organic carbon, median = 14.2 μmol L<sup>-1</sup>, <italic>n</italic> = 25; chlorophyll <italic>a</italic>: median = 2.0 nmol L<sup>-1</sup>, <italic>n</italic> = 23) pointing to regulatory mechanisms of the heme <italic>b</italic> pool for growth conservation. Dissolved iron (DFe) was not depleted (SML: median = 0.38 nmol L<sup>-1</sup>, <italic>n</italic> = 11) in the Irminger Basin, but large diatoms (<italic>Rhizosolenia</italic> sp.) dominated. Hence, heme <italic>b</italic> 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 <italic>b</italic> concentrations found in the Iceland Basin and Labrador Sea (median = 3.4 pmol L<sup>-1</sup>, <italic>n</italic> = 20), despite having similar DFe concentrations to the Irminger Basin, were attributed to an earlier growth phase of the extant phytoplankton populations. Thus, heme <italic>b</italic> provides a snapshot of the cellular activity <italic>in situ</italic> and could both be used as indicator of iron limitation and contribute to understanding phytoplankton adaptation mechanisms to changing iron supplies.</p>