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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-FIB-SEM imaging of vitrified E. huxleyi reveals coccolith calciteand calcium-rich bodies in separate compartments.(a–d) Two slices from the same cell acquired with in-lenssecondary electron detector (a,c) and energy selectivebackscattered electron detector (b,c) showing across-sectioned coccolith in statu nascendi (blue), the Ca-rich body(red), the coccolith vesicle (CV)–reticular body system (RB), thenucleus (N) and the chloroplast (Chl). Additional organelles are visible inthe secondary electron images as is shown in Supplementary Fig. 3. (e)Oversampled and contrast-enhanced magnification of the area framed inc, illustrating the membrane that encloses the Ca-rich body(arrows). (f) 3D reconstruction of an E. huxleyi cell from acryo-FIB-SEM image series, showing the nucleus (violet), chloroplast (darkgreen), plasma membrane (light green), a coccolith in statu nascendi(blue), Ca-rich bodies (red) and the membranes encompassing Ca-rich bodies(orange). Figure is accompanied by Supplementary Video 2.
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f3: Cryo-FIB-SEM imaging of vitrified E. huxleyi reveals coccolith calciteand calcium-rich bodies in separate compartments.(a–d) Two slices from the same cell acquired with in-lenssecondary electron detector (a,c) and energy selectivebackscattered electron detector (b,c) showing across-sectioned coccolith in statu nascendi (blue), the Ca-rich body(red), the coccolith vesicle (CV)–reticular body system (RB), thenucleus (N) and the chloroplast (Chl). Additional organelles are visible inthe secondary electron images as is shown in Supplementary Fig. 3. (e)Oversampled and contrast-enhanced magnification of the area framed inc, illustrating the membrane that encloses the Ca-rich body(arrows). (f) 3D reconstruction of an E. huxleyi cell from acryo-FIB-SEM image series, showing the nucleus (violet), chloroplast (darkgreen), plasma membrane (light green), a coccolith in statu nascendi(blue), Ca-rich bodies (red) and the membranes encompassing Ca-rich bodies(orange). Figure is accompanied by Supplementary Video 2.

Mentions: To elucidate the ultrastructural environment of the Ca-rich body at higherresolution, we imaged cryo-fixed cells by serial FIB milling and block face SEMat cryo-condition using a Zeiss Auriga60 FIB-SEM23. In the energyselective backscattered (EsB) electron images, the Ca-rich bodies and coccolithsin statu nascendi were easily identifiable due to their calcite-likecontrast (Fig. 3b,d). Image analysis, using coccolithcalcite (calcium concentration is 27 M) and culture medium (calciumconcentration is 10 mM) as Ca reference concentrations, yielded aconcentration of 10 M Ca for the body, which is in range of theconcentration determined from our X-ray tomography data set. In the in-lenssecondary electron images, membrane-bound compartments were clearly visible(Fig. 3a,c). Most interestingly, a membrane was foundin close proximity with the Ca-rich body, visible as thin dark line (Fig. 3c,e). Manual segmentation of this membrane in theimage stacks revealed it to encompass the Ca-rich body, forming a compartment(Fig. 3f). Careful inspection of all images in thestacks found no connection between this compartment and the coccolithvesicle–reticular body system or any other visible endomembrane system.Noteworthy, the compartment was always larger than the enclosed Ca-rich body andthe largest compartment had a volume of 1.5 μm3. Ifthe largest compartment would be filled entirely with calcium at a concentrationof 10 M, as in the Ca-rich body, it would store 15 fmol Ca, whichis about two-third of the Ca required for a full coccolith.


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-FIB-SEM imaging of vitrified E. huxleyi reveals coccolith calciteand calcium-rich bodies in separate compartments.(a–d) Two slices from the same cell acquired with in-lenssecondary electron detector (a,c) and energy selectivebackscattered electron detector (b,c) showing across-sectioned coccolith in statu nascendi (blue), the Ca-rich body(red), the coccolith vesicle (CV)–reticular body system (RB), thenucleus (N) and the chloroplast (Chl). Additional organelles are visible inthe secondary electron images as is shown in Supplementary Fig. 3. (e)Oversampled and contrast-enhanced magnification of the area framed inc, illustrating the membrane that encloses the Ca-rich body(arrows). (f) 3D reconstruction of an E. huxleyi cell from acryo-FIB-SEM image series, showing the nucleus (violet), chloroplast (darkgreen), plasma membrane (light green), a coccolith in statu nascendi(blue), Ca-rich bodies (red) and the membranes encompassing Ca-rich bodies(orange). Figure is accompanied by Supplementary Video 2.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: Cryo-FIB-SEM imaging of vitrified E. huxleyi reveals coccolith calciteand calcium-rich bodies in separate compartments.(a–d) Two slices from the same cell acquired with in-lenssecondary electron detector (a,c) and energy selectivebackscattered electron detector (b,c) showing across-sectioned coccolith in statu nascendi (blue), the Ca-rich body(red), the coccolith vesicle (CV)–reticular body system (RB), thenucleus (N) and the chloroplast (Chl). Additional organelles are visible inthe secondary electron images as is shown in Supplementary Fig. 3. (e)Oversampled and contrast-enhanced magnification of the area framed inc, illustrating the membrane that encloses the Ca-rich body(arrows). (f) 3D reconstruction of an E. huxleyi cell from acryo-FIB-SEM image series, showing the nucleus (violet), chloroplast (darkgreen), plasma membrane (light green), a coccolith in statu nascendi(blue), Ca-rich bodies (red) and the membranes encompassing Ca-rich bodies(orange). Figure is accompanied by Supplementary Video 2.
Mentions: To elucidate the ultrastructural environment of the Ca-rich body at higherresolution, we imaged cryo-fixed cells by serial FIB milling and block face SEMat cryo-condition using a Zeiss Auriga60 FIB-SEM23. In the energyselective backscattered (EsB) electron images, the Ca-rich bodies and coccolithsin statu nascendi were easily identifiable due to their calcite-likecontrast (Fig. 3b,d). Image analysis, using coccolithcalcite (calcium concentration is 27 M) and culture medium (calciumconcentration is 10 mM) as Ca reference concentrations, yielded aconcentration of 10 M Ca for the body, which is in range of theconcentration determined from our X-ray tomography data set. In the in-lenssecondary electron images, membrane-bound compartments were clearly visible(Fig. 3a,c). Most interestingly, a membrane was foundin close proximity with the Ca-rich body, visible as thin dark line (Fig. 3c,e). Manual segmentation of this membrane in theimage stacks revealed it to encompass the Ca-rich body, forming a compartment(Fig. 3f). Careful inspection of all images in thestacks found no connection between this compartment and the coccolithvesicle–reticular body system or any other visible endomembrane system.Noteworthy, the compartment was always larger than the enclosed Ca-rich body andthe largest compartment had a volume of 1.5 μm3. Ifthe largest compartment would be filled entirely with calcium at a concentrationof 10 M, as in the Ca-rich body, it would store 15 fmol Ca, whichis about two-third of the Ca required for a full coccolith.

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