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A vacuole-like compartment concentrates a disordered calcium phase in a key coccolithophorid alga.

Sviben S, Gal A, Hood MA, Bertinetti L, Politi Y, Bennet M, Krishnamoorthy P, Schertel A, Wirth R, Sorrentino A, Pereiro E, Faivre D, Scheffel A - Nat Commun (2016)

Bottom Line: We identify a compartment, distinct from the coccolith-producing compartment, filled with high concentrations of a disordered form of calcium.The amounts of calcium stored in this reservoir seem to be dynamic and at a certain stage the compartment is in direct contact with the coccolith-producing vesicle, suggesting an active role in coccolith formation.Our findings provide insights into calcium accumulation in this important calcifying organism.

View Article: PubMed Central - PubMed

Affiliation: Max-Planck Institute of Molecular Plant Physiology, Potsdam-Golm 14476, Germany.

ABSTRACT
Coccoliths are calcitic particles produced inside the cells of unicellular marine algae known as coccolithophores. They are abundant components of sea-floor carbonates, and the stoichiometry of calcium to other elements in fossil coccoliths is widely used to infer past environmental conditions. Here we study cryo-preserved cells of the dominant coccolithophore Emiliania huxleyi using state-of-the-art nanoscale imaging and spectroscopy. We identify a compartment, distinct from the coccolith-producing compartment, filled with high concentrations of a disordered form of calcium. Co-localized with calcium are high concentrations of phosphorus and minor concentrations of other cations. The amounts of calcium stored in this reservoir seem to be dynamic and at a certain stage the compartment is in direct contact with the coccolith-producing vesicle, suggesting an active role in coccolith formation. Our findings provide insights into calcium accumulation in this important calcifying organism.

No MeSH data available.


Related in: MedlinePlus

Cryo-X-ray imaging reveals concentrated calcium pools in E. huxleyicells.(a) Two-dimensional slices from a reconstructed X-ray tomogram with(top) an immature coccolith marked by the arrowhead and a calcium-rich bodymarked by the arrow, and (bottom) with 3D segmentation of the calcium-richbodies (red) and intracellular coccoliths (blue). (b) X-ray imagesrecorded at an energy below the Ca L2,3-egde (342 eV), atthe edge energy (353.2 eV) and the grey value difference between bothimages. (c) Averaged XANES spectra of the Ca L2,3-edge.For each spectrum, data from the relevant pixels of four cells wereaveraged; the inset shows the exact locations in one of these cells. Noticethe difference in the position of the crystal field peak (vertical lines)between coccolith calcite and synthetic calcium phosphate. Figure isaccompanied by Supplementary Movie1.
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f2: Cryo-X-ray imaging reveals concentrated calcium pools in E. huxleyicells.(a) Two-dimensional slices from a reconstructed X-ray tomogram with(top) an immature coccolith marked by the arrowhead and a calcium-rich bodymarked by the arrow, and (bottom) with 3D segmentation of the calcium-richbodies (red) and intracellular coccoliths (blue). (b) X-ray imagesrecorded at an energy below the Ca L2,3-egde (342 eV), atthe edge energy (353.2 eV) and the grey value difference between bothimages. (c) Averaged XANES spectra of the Ca L2,3-edge.For each spectrum, data from the relevant pixels of four cells wereaveraged; the inset shows the exact locations in one of these cells. Noticethe difference in the position of the crystal field peak (vertical lines)between coccolith calcite and synthetic calcium phosphate. Figure isaccompanied by Supplementary Movie1.

Mentions: To directly observe the putative amorphous Ca phases, we investigatedcryo-preserved E. huxleyi cells using synchrotron soft X-ray tomographyand spectromicroscopy. The minimal sample preparation procedure, consisting onlyof dissolving extracellular coccoliths and vitrification of cells after denovo coccolith formation had started, allowed the visualization of theinternal organization of the cells during coccolith production in a yetunprecedented close-to-native state. Reconstruction of tilt-series images takenat an X-ray energy of 520 eV yielded three-dimensional (3D) data with acalculated spatial resolution of 52 nm, half pitch. At this energy,C-rich and Ca-rich moieties are more absorptive than aqueous solutions andtherefore concentrated organic and inorganic matter appear dark, whereas thecytosol appears bright1718. The tomograms revealedintracellular bodies with highly absorbing material, similar to the calcite ofcoccoliths, which were always spatially separated from the coccolith in statunascendi (Fig. 2a). We probed the Ca content ofthese bodies by imaging cells at 342 eV, which is below the CaL2,3-edge where calcium is virtually transparent, and at353.2 eV, which is above the Ca absorption edge19. Thedifference images of the two energies revealed a distinct Ca-rich body inaddition to a forming coccolith in the cells (Fig. 2b). Tocharacterize the Ca phase of the bodies, we acquired spatially resolved CaL2,3-edge XANES spectra by sequentially imaging the same field ofview and varying the energy across the Ca L2,3-edge. Averaged spectraextracted from coccoliths in statu nascendi showed the characteristicspectrum of calcite (Fig. 2c). For reason explained below,we also acquired Ca L2,3-edge XANES spectra from synthetic, poorlycrystalline calcium phosphate (Fig. 2c). The averagedspectra extracted from the Ca-rich bodies lacked significant peaks at the energyof the calcite crystal field peaks (at 347.9 and 351.3 eV) or thehydroxyapatite crystal field peaks (at 348.1 and 351.5 eV), suggestingthat the body contains an amorphous calcium phase19202122.On the basis of the absorbance intensity at the Ca edge, which is proportionalto the Ca content in the beam path and the volume of the Ca-rich body, theaverage calcium concentration in the body was determined to be∼13.4±2.3 M.


A vacuole-like compartment concentrates a disordered calcium phase in a key coccolithophorid alga.

Sviben S, Gal A, Hood MA, Bertinetti L, Politi Y, Bennet M, Krishnamoorthy P, Schertel A, Wirth R, Sorrentino A, Pereiro E, Faivre D, Scheffel A - Nat Commun (2016)

Cryo-X-ray imaging reveals concentrated calcium pools in E. huxleyicells.(a) Two-dimensional slices from a reconstructed X-ray tomogram with(top) an immature coccolith marked by the arrowhead and a calcium-rich bodymarked by the arrow, and (bottom) with 3D segmentation of the calcium-richbodies (red) and intracellular coccoliths (blue). (b) X-ray imagesrecorded at an energy below the Ca L2,3-egde (342 eV), atthe edge energy (353.2 eV) and the grey value difference between bothimages. (c) Averaged XANES spectra of the Ca L2,3-edge.For each spectrum, data from the relevant pixels of four cells wereaveraged; the inset shows the exact locations in one of these cells. Noticethe difference in the position of the crystal field peak (vertical lines)between coccolith calcite and synthetic calcium phosphate. Figure isaccompanied by Supplementary Movie1.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4834641&req=5

f2: Cryo-X-ray imaging reveals concentrated calcium pools in E. huxleyicells.(a) Two-dimensional slices from a reconstructed X-ray tomogram with(top) an immature coccolith marked by the arrowhead and a calcium-rich bodymarked by the arrow, and (bottom) with 3D segmentation of the calcium-richbodies (red) and intracellular coccoliths (blue). (b) X-ray imagesrecorded at an energy below the Ca L2,3-egde (342 eV), atthe edge energy (353.2 eV) and the grey value difference between bothimages. (c) Averaged XANES spectra of the Ca L2,3-edge.For each spectrum, data from the relevant pixels of four cells wereaveraged; the inset shows the exact locations in one of these cells. Noticethe difference in the position of the crystal field peak (vertical lines)between coccolith calcite and synthetic calcium phosphate. Figure isaccompanied by Supplementary Movie1.
Mentions: To directly observe the putative amorphous Ca phases, we investigatedcryo-preserved E. huxleyi cells using synchrotron soft X-ray tomographyand spectromicroscopy. The minimal sample preparation procedure, consisting onlyof dissolving extracellular coccoliths and vitrification of cells after denovo coccolith formation had started, allowed the visualization of theinternal organization of the cells during coccolith production in a yetunprecedented close-to-native state. Reconstruction of tilt-series images takenat an X-ray energy of 520 eV yielded three-dimensional (3D) data with acalculated spatial resolution of 52 nm, half pitch. At this energy,C-rich and Ca-rich moieties are more absorptive than aqueous solutions andtherefore concentrated organic and inorganic matter appear dark, whereas thecytosol appears bright1718. The tomograms revealedintracellular bodies with highly absorbing material, similar to the calcite ofcoccoliths, which were always spatially separated from the coccolith in statunascendi (Fig. 2a). We probed the Ca content ofthese bodies by imaging cells at 342 eV, which is below the CaL2,3-edge where calcium is virtually transparent, and at353.2 eV, which is above the Ca absorption edge19. Thedifference images of the two energies revealed a distinct Ca-rich body inaddition to a forming coccolith in the cells (Fig. 2b). Tocharacterize the Ca phase of the bodies, we acquired spatially resolved CaL2,3-edge XANES spectra by sequentially imaging the same field ofview and varying the energy across the Ca L2,3-edge. Averaged spectraextracted from coccoliths in statu nascendi showed the characteristicspectrum of calcite (Fig. 2c). For reason explained below,we also acquired Ca L2,3-edge XANES spectra from synthetic, poorlycrystalline calcium phosphate (Fig. 2c). The averagedspectra extracted from the Ca-rich bodies lacked significant peaks at the energyof the calcite crystal field peaks (at 347.9 and 351.3 eV) or thehydroxyapatite crystal field peaks (at 348.1 and 351.5 eV), suggestingthat the body contains an amorphous calcium phase19202122.On the basis of the absorbance intensity at the Ca edge, which is proportionalto the Ca content in the beam path and the volume of the Ca-rich body, theaverage calcium concentration in the body was determined to be∼13.4±2.3 M.

Bottom Line: We identify a compartment, distinct from the coccolith-producing compartment, filled with high concentrations of a disordered form of calcium.The amounts of calcium stored in this reservoir seem to be dynamic and at a certain stage the compartment is in direct contact with the coccolith-producing vesicle, suggesting an active role in coccolith formation.Our findings provide insights into calcium accumulation in this important calcifying organism.

View Article: PubMed Central - PubMed

Affiliation: Max-Planck Institute of Molecular Plant Physiology, Potsdam-Golm 14476, Germany.

ABSTRACT
Coccoliths are calcitic particles produced inside the cells of unicellular marine algae known as coccolithophores. They are abundant components of sea-floor carbonates, and the stoichiometry of calcium to other elements in fossil coccoliths is widely used to infer past environmental conditions. Here we study cryo-preserved cells of the dominant coccolithophore Emiliania huxleyi using state-of-the-art nanoscale imaging and spectroscopy. We identify a compartment, distinct from the coccolith-producing compartment, filled with high concentrations of a disordered form of calcium. Co-localized with calcium are high concentrations of phosphorus and minor concentrations of other cations. The amounts of calcium stored in this reservoir seem to be dynamic and at a certain stage the compartment is in direct contact with the coccolith-producing vesicle, suggesting an active role in coccolith formation. Our findings provide insights into calcium accumulation in this important calcifying organism.

No MeSH data available.


Related in: MedlinePlus