Distinguishing between extra‐ and intracellular iron in marine phytoplankton.

Hudson, Robert J.; Morel, François M. M.

doi:10.4319/lo.1989.34.6.1113

Cited by 206 publications

(147 citation statements)

References 7 publications

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“…2C) exhibited significant desorption from the bacteria cells over the first 12 h, with relative equilibration thereafter at about 40% dissolved 234 Th. Th was associated primarily with the external surfaces of the bacteria cells (80 to 85% of bacterial 234 Th was removable by rinsing with Ti(III) EDTA-citrate solution; Hudson & Morel 1989). These results suggested that Th was in reversible equilibrium between the cell surface and dissolved phase.…”

Section: Model System Studymentioning

confidence: 68%

Remineralization and recycling of iron, thorium and organic carbon by heterotrophic marine protists in culture

Barbeau¹,

Kujawinski²,

Moffett³

2001

Aquat. Microb. Ecol.

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To characterize trace metal cycling in marine systems as mediated by heterotrophic protists, we conducted a series of laboratory experiments in 2-organism model systems consisting of bacteria and protistan grazers. Trace metal isotopes ( 59 Fe and 234 Th), 14 C, and bulk organic carbon measurements were used to follow the chemical transformation of bacterial carbon and associated trace metals by several different grazer species. Results indicate that grazers were able to cause repartitioning of Th and regeneration of Fe from bacterial prey into the dissolved phase (< 0.2 µm), even in particle-rich laboratory cultures. For both Th and Fe, protist grazing led to the formation of relatively stable dissolved and colloidal metal-organic species. Metal/carbon ratios of the particle pool in some model systems with grazers were significantly altered, indicating a decoupling of trace metal and organic carbon cycling through the grazing process. Different protist species exhibited substantial variation (up to a factor of 10) in their ability to quantitatively remobilize trace metals from bacterial prey. The implications of these findings for trace metal cycling in marine systems are discussed. KEY WORDS: Marine protists · Iron · Thorium · Organic carbon · RecyclingResale or republication not permitted without written consent of the publisher Aquat Microb Ecol 24: 69-81, 2001 suggests that the effect of protist grazing on trace metals in the oceans is both geochemically and ecologically significant.This study presents some of the first data on the regeneration and recycling of cell-associated Fe and Th isotopes in conjunction with cellular organic carbon by heterotrophic protists in laboratory culture. Despite the widespread use of naturally occurring Th isotopes as analogues for particle-reactive species (Clegg & Whitfield 1991, Gustafsson et al. 1997) and as tracers of particulate organic carbon (POC) export from the upper ocean (e.g. Buesseler et al. 1992, Murray et al. 1996, almost nothing is known about the actual mechanism of Th cycling via protists and associated organisms of the 'microbial loop'. Very few model system studies have examined the mechanism of Fe recycling in seawater via protistan grazing (Hutchins & Bruland 1994, Chase & Price 1997. Both of these studies employed the grazer Paraphysomonas sp. In the present study several different grazer species (including Paraphysomonas) were examined in terms of Fe, Th and organic carbon remineralization.In the first experiment, a model system study, the size fractionation of Fe and Th isotopes and organic carbon was followed as a heterotrophic nanoflagellate (Cafeteria sp., a free-living flagellate 3-5 µm diameter) consumed bacterial prey. Next a sequence of experiments was conducted in order to determine the relative abilities of 3 different kinds of protists to remobilize cell-associated Fe and Th (Cafeteria sp.; Uronema sp., a benthic scuticociliate 7-15 µm in length; and Paraphysomonas imperforata, a free-living flagellate 5-7 µm in diameter, whic...

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Section: Model System Studymentioning

confidence: 68%

Remineralization and recycling of iron, thorium and organic carbon by heterotrophic marine protists in culture

Barbeau¹,

Kujawinski²,

Moffett³

2001

Aquat. Microb. Ecol.

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“…The colonies were filtered onto a polycarbonate filter (0.2-0.8 m) after the incubation, rinsed with a titanium-ethylenediamine-tetraacetic acid-citrate reagent to remove any extracellular 55 Fe (Hudson and Morel 1989), and rinsed with seawater. The Fe uptake rate was determined for each incubation vial by measuring the 55 Fe incorporated into the cells by liquid scintillation counting.…”

Section: Methodsmentioning

confidence: 99%

Bioavailability of iron to Trichodesmium colonies in the western subtropical Atlantic Ocean

Achilles

Church

Wilhelm

et al. 2003

Limnology & Oceanography

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Trichodesmium provides new nitrogen (N) to marine surface waters via N 2 fixation, a process that requires a substantial amount of iron (Fe). Organic ligands in seawater that bind Fe could either increase or reduce the bioavailability of Fe. Electrochemical techniques indicate that these naturally occurring ligands have Fe-binding constants similar to those of siderophores and porphyrins, suggesting that these chelators play an important role in determining the bioavailability of Fe to cyanobacteria. We conducted Fe uptake experiments using model ligands labeled with 55 Fe to compare the bioavailability of inorganic Fe(III), porphyrin-bound Fe(III), and siderophorebound Fe(III) to field-collected Trichodesmium colonies. Inorganic Fe(III) and siderophore-bound Fe(III) were more bioavailable to Trichodesmium colonies than was porphyrin-bound Fe(III). Furthermore, the bioavailability of the siderophore-bound Fe(III) can be characterized by the functional groups of the siderophore. The dihydroxamate siderophore and an uncharacterized ligand from a cultured Synechococcus sp. increased the bioavailability of Fe compared to the trihydroxamate siderophores. Except for experiments with desferrioxamine B, dark incubations resulted in lower Fe uptake rates for all treatments, relative to parallel lighted incubations. This suggests that light enhances the photochemical dissociation of most of the ligand complexes or that light energy is required for the active transport of Fe complexed to the model ligands. The Fe uptake rate of Trichodesmium colonies also differed slightly on the basis of colony morphology, with higher uptake rates with ''puffs'' than ''tufts.'' These experiments show that Trichodesmium colonies are capable of discriminating between Fe bound to different organic complexes.

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“…Changes in climate-driven biogeochemical processes such as photosynthesis, calcification, nitrogen fixation and silicification have been investigated in the laboratory (on land and at sea) by manipulating environmental variables including macro- (Krauk et al 2006) and micronutrients (Hudson & Morel 1989;Timmermans et al 1994;Yoshida et al 2002), and carbonate chemistry (Zondervan et al 2001). However, we face two main problems in interpreting the laboratory data.…”

Section: (A ) Laboratory Experimentsmentioning

confidence: 99%

Ocean fertilization: a potential means of geoengineering?

Lampitt

Achterberg

Anderson

et al. 2008

Phil. Trans. R. Soc. A.

153

125

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The oceans sequester carbon from the atmosphere partly as a result of biological productivity. Over much of the ocean surface, this productivity is limited by essential nutrients and we discuss whether it is likely that sequestration can be enhanced by supplying limiting nutrients. Various methods of supply have been suggested and we discuss the efficacy of each and the potential side effects that may develop as a result. Our conclusion is that these methods have the potential to enhance sequestration but that the current level of knowledge from the observations and modelling carried out to date does not provide a sound foundation on which to make clear predictions or recommendations. For ocean fertilization to become a viable option to sequester CO 2 , we need more extensive and targeted fieldwork and better mathematical models of ocean biogeochemical processes. Models are needed both to interpret field observations and to make reliable predictions about the side effects of large-scale fertilization. They would also be an essential tool with which to verify that sequestration has effectively taken place. There is considerable urgency to address climate change mitigation and this demands that new fieldwork plans are developed rapidly. In contrast to previous experiments, these must focus on the specific objective which is to assess the possibilities of CO 2 sequestration through fertilization.

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Distinguishing between extra‐ and intracellular iron in marine phytoplankton.

Cited by 206 publications

References 7 publications

Remineralization and recycling of iron, thorium and organic carbon by heterotrophic marine protists in culture

Remineralization and recycling of iron, thorium and organic carbon by heterotrophic marine protists in culture

Bioavailability of iron to Trichodesmium colonies in the western subtropical Atlantic Ocean

Ocean fertilization: a potential means of geoengineering?

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