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  • 1
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    Heme b in marine phytoplankton and particulate material from the North Atlantic Ocean (2013)
    Inter Research
    In:  Marine Ecology Progress Series, 483 . pp. 1-17.
    Details
    Publication Date: 2017-10-24
    Description: Concentrations of heme b, the ironcontaining prosthetic group of many hemoproteins, were measured in 6 species of marine phytoplankton (Dunaliella tertiolecta, Emiliania huxleyi, Thalassio - sira weissflogii, T. oceanica, Phaeodactylum tricor - nutum and Synechococcus sp. WH7803) that were subjected to variations in iron concentration. Changes in heme b in response to reduced light and nitrate were also ex amined for E. huxleyi and T. oceanica. Results from laboratory cultures were compared with heme b determined in particulate material in the North Atlantic. In cultures, heme b made up 18 ± 14% (SE) of the total iron pool. Reduced iron and nitrate concentrations resulted in a decreased intracellular heme b concentration, expressed as per mole carbon. Chlorophyll a (chl a) to heme b ratios in E. huxleyi and D. tertiolecta in creased in response to limited light and nutrient availability, but slightly decreased or did not change in the diatoms and the cyanophyte Synechococcus sp. WH7803. The heme b:particulate organic carbon (POC) and chl a:heme b ratios in the North Atlantic were within the range observed in phytoplankton cultures. In the surface mixed layer, decreases in heme b:POC ratios were linked to decreases in nutrient concentrations. Chl a:heme b ratios increased with depth and were thus primarily affected by light availability. Relative relationships between heme b, chl a and POC in the North Atlantic likely represented a change in the ability of cells to undertake cellular processes driven by chl a (light harvesting) and heme b (e.g. electron transport) according to ambient light and nutrient conditions.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3354/meps10367
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Transition Metals and Heavy Metal Speciation (2019)
    Academic Press
    In:  In: Encyclopedia of Ocean Sciences, 3rd edition. , ed. by Cochran, J. K. Academic Press, London, pp. 218-227. ISBN 978-0-12-813081-0
    Details
    Publication Date: 2020-01-14
    Description: Transition metals and trace metals enter the ocean via river runoff, wind-blown dust, diffusion from sediments, hydrothermal inputs and anthropogenic activities. Some of these metals (e.g., Fe, Mn, Co) are essential micronutrients needed by phytoplankton. Micronutrient metals, as well as metals like Hg, Pb, and Ag, which have no biochemical role, can be toxic at enhanced concentrations. The chemical and physical speciation of the metals determines their geochemical behavior and availability to marine microorganisms. Complexation by inorganic and organic ligands hence has a strong influence on metal behavior. The GEOTRACES Programme is transforming our global view of metal behavior, sinks and sources in the ocean, through detailed observations along full ocean sections.
    Type: Book chapter , NonPeerReviewed
    DOI: 10.1016/B978-0-12-409548-9.11394-6
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    OceanRep: Book chapter
  • 3
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    Heme b quotas are low in Southern Ocean phytoplankton (2015)
    Inter Research
    In:  Marine Ecology Progress Series, 532 . pp. 29-40.
    Details
    Publication Date: 2021-04-23
    Description: Heme is the iron-containing prosthetic group of hemoproteins, and is thus required for photosynthesis, respiration and nitrate reduction in marine phytoplankton. Here we report concentrations of heme b in Southern Ocean phytoplankton and contrast our findings with those in coastal species. The concentration of particulate heme b (pmol l-1) observed at the end of the exponential growth phase was related to the concentration of dissolved iron in the culture media. Small Southern Ocean phytoplankton species (〈6 μm in diameter) had heme b quotas 〈1 μmol mol-1 carbon, the lowest yet reported for marine phytoplankton. Heme b was also depleted in these species with respect to chlorophyll a. We calculated the amount of carbon accumulated per mole of heme b per second in our cultures (heme growth efficiency, HGE) and found that small Southern Ocean species can maintain growth rates, even while heme b content is reduced. Small Southern Ocean phytoplankton can thus produce more particulate carbon than larger Southern Ocean or small coastal species at equivalent iron concentrations. Combining primary productivity and heme b concentrations reported for the open ocean, we found that HGE in natural populations was within the range of our laboratory culture results. HGE was also observed to be higher at open ocean stations characterized by low iron concentrations. Our results suggest that low heme b quotas do not necessarily result in reduced growth and that marine phytoplankton can optimize iron use by manipulating the intracellular hemoprotein pool
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3354/meps11345
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Stoichiometry of Fe, Mn and Co in the marine diazotroph Crocosphaera subtropica ATCC51142 in Fe- and P-limited continuous cultures (2020)
    Inter Research
    Details
    Publication Date: 2023-02-08
    Description: We investigated trace element stoichiometries of the nitrogen-fixing marine cyanobacterium Crocosphaera subtropica ATCC51142 under steady-state growth conditions. We utilized exponentially fed batch cultures and varied iron (Fe) concentrations to establish nutrient limitation in C. subtropica growing at a constant growth rate (0.11 d -1 ). No statistical difference in cell density, chlorophyll a , particulate organic carbon (C), nitrogen (N) and phosphorus (P) were observed between consecutive days after Day 14, and cultures were assumed to be at steady state with respect to growth for the remaining 11 d of the experiment. Cultures were limited by P in the highest Fe treatment (41 nmol l -1 ) and by Fe in the 2 lower-concentration Fe treatments (1 and 5 nmol l -1 ). Cell size and in vivo fluorescence changed throughout the experiment in the 1 nmol l -1 Fe treatment, suggesting ongoing acclimation of C. subtropica to our lowest Fe supply. Nevertheless, Fe:C ratios were not significantly different between the Fe treatments, and we calculated an average (±SD) Fe:C ratio of 32 ± 14 µmol mol -1 for growth at 0.11 d -1 . Steady-state P-limited cells had lower P quotas, whilst Fe-limited cells had higher manganese (Mn) and cobalt (Co) quotas. We attribute the increase in Mn and Co quotas at low Fe to a competitive effect resulting from changes in the supply ratio of trace elements. Such an effect has implications for variability in elemental stoichiometry in marine phytoplankton, and potential consequences for trace metal uptake and cycling in marine systems.
    Type: Article , PeerReviewed
    Format: text
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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