Limits...
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

Ultrastructural and elemental microanalysis of the calcium-rich body.(a) HAADF-STEM image of a thin-sectioned cell showing the nucleus (N),the chloroplast (Chl), the coccolith vesicle (CV)–reticular bodysystem (RB) (encircled by the white line), coccolith calcite (bluearrowhead) and the Ca-rich body (red arrow). Additional organelles that arevisible in the HAADF-STEM images are shown in Supplementary Fig. 4. (b)High-resolution images and corresponding Fourier-transformed image ofcoccolith calcite and the Ca-rich body. (c) STEM-EELS spectrameasured at the carbon K-edge on the Ca-rich body, coccolith calcite andembedding resin. (d) STEM-EDX spectra of the Ca-rich body andcoccolith calcite.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4834641&req=5

f4: Ultrastructural and elemental microanalysis of the calcium-rich body.(a) HAADF-STEM image of a thin-sectioned cell showing the nucleus (N),the chloroplast (Chl), the coccolith vesicle (CV)–reticular bodysystem (RB) (encircled by the white line), coccolith calcite (bluearrowhead) and the Ca-rich body (red arrow). Additional organelles that arevisible in the HAADF-STEM images are shown in Supplementary Fig. 4. (b)High-resolution images and corresponding Fourier-transformed image ofcoccolith calcite and the Ca-rich body. (c) STEM-EELS spectrameasured at the carbon K-edge on the Ca-rich body, coccolith calcite andembedding resin. (d) STEM-EDX spectra of the Ca-rich body andcoccolith calcite.

Mentions: We investigated the thin sections of high-pressure frozen, cryo-substituted andresin-embedded E. huxleyi cells using high-angle annular dark-fieldscanning transmission electron microscopy (HAADF-STEM) and analysed theelemental composition by energy-dispersive X-ray (EDX) spectroscopy and electronenergy loss spectroscopy (EELS) at positions of interest. HAADF-STEM is suitedfor the imaging of the non-stained thin sections, as the image contrast isrelated to the atomic number of the elements in the beam path24.Calcium appears therefore brighter than biomolecules. We observed electron-denseCa-rich bodies in the thin sections collected in ethylene glycol (Fig. 4a) but not in the sections collected in water. The dissolutionof the bodies in water was accompanied by the dissolution of the coccolithcalcite crystals, leaving an impression in the embedding resin. The same hasbeen noticed previously by others12. The use of water forcollecting the thin sections may therefore be the reason why the Ca-rich bodywas not observed in previous cytological studies in which occasionally aspacious intracellular compartment was observed but designated aschrysolaminarin vesicle10 or vacuole25 due to itshighly electron transparent content, which most likely dissolved during samplepreparation and could have been the Ca-rich body. When imaging the body at highmagnification, no lattice fringes were observed, supporting our X-rayspectroscopy conclusion that the Ca in the body is in an amorphous phase (Fig. 4b). The carbon K-edge EELS spectra of the Ca-rich bodywas distinct from both coccolith calcite and the embedding resin, suggestingthat the body does not contain significant amounts of calcium carbonate (Fig. 4c). Interestingly, the spectrum of the body showed asmall peak at 288.2 eV, which has been previously associated with amidecarbonyl bonds and suggests the presence of proteins26. To oursurprise, the EDX analysis revealed the Ca-rich bodies to contain very highamounts of P in addition to Ca and minor amounts of other elements (Fig. 4d). Among these elements was magnesium, an importanttrace element in coccolith calcite, whose amount relative to calcium is used toinfer past climatic conditions5. The excess of P over Ca in theCa-rich body (Supplementary Table1) suggests that Ca is bound by phosphate-rich macromolecules. Becausethe amount of P exceeds the amount of carbon, the most plausible candidates arenot phosphorylated biomolecules but rather polyphosphates, which have beenproposed to play a role in CaCO3 biomineralization27and were discovered already in the non-calcifying relative of E. huxleyi,Pavlova ennorea sp. nov.28. In E. huxleyipolyphosphates may be synthesized by the enzyme polyphosphate polymerase (JGIID406855)29.


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)

Ultrastructural and elemental microanalysis of the calcium-rich body.(a) HAADF-STEM image of a thin-sectioned cell showing the nucleus (N),the chloroplast (Chl), the coccolith vesicle (CV)–reticular bodysystem (RB) (encircled by the white line), coccolith calcite (bluearrowhead) and the Ca-rich body (red arrow). Additional organelles that arevisible in the HAADF-STEM images are shown in Supplementary Fig. 4. (b)High-resolution images and corresponding Fourier-transformed image ofcoccolith calcite and the Ca-rich body. (c) STEM-EELS spectrameasured at the carbon K-edge on the Ca-rich body, coccolith calcite andembedding resin. (d) STEM-EDX spectra of the Ca-rich body andcoccolith calcite.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Ultrastructural and elemental microanalysis of the calcium-rich body.(a) HAADF-STEM image of a thin-sectioned cell showing the nucleus (N),the chloroplast (Chl), the coccolith vesicle (CV)–reticular bodysystem (RB) (encircled by the white line), coccolith calcite (bluearrowhead) and the Ca-rich body (red arrow). Additional organelles that arevisible in the HAADF-STEM images are shown in Supplementary Fig. 4. (b)High-resolution images and corresponding Fourier-transformed image ofcoccolith calcite and the Ca-rich body. (c) STEM-EELS spectrameasured at the carbon K-edge on the Ca-rich body, coccolith calcite andembedding resin. (d) STEM-EDX spectra of the Ca-rich body andcoccolith calcite.
Mentions: We investigated the thin sections of high-pressure frozen, cryo-substituted andresin-embedded E. huxleyi cells using high-angle annular dark-fieldscanning transmission electron microscopy (HAADF-STEM) and analysed theelemental composition by energy-dispersive X-ray (EDX) spectroscopy and electronenergy loss spectroscopy (EELS) at positions of interest. HAADF-STEM is suitedfor the imaging of the non-stained thin sections, as the image contrast isrelated to the atomic number of the elements in the beam path24.Calcium appears therefore brighter than biomolecules. We observed electron-denseCa-rich bodies in the thin sections collected in ethylene glycol (Fig. 4a) but not in the sections collected in water. The dissolutionof the bodies in water was accompanied by the dissolution of the coccolithcalcite crystals, leaving an impression in the embedding resin. The same hasbeen noticed previously by others12. The use of water forcollecting the thin sections may therefore be the reason why the Ca-rich bodywas not observed in previous cytological studies in which occasionally aspacious intracellular compartment was observed but designated aschrysolaminarin vesicle10 or vacuole25 due to itshighly electron transparent content, which most likely dissolved during samplepreparation and could have been the Ca-rich body. When imaging the body at highmagnification, no lattice fringes were observed, supporting our X-rayspectroscopy conclusion that the Ca in the body is in an amorphous phase (Fig. 4b). The carbon K-edge EELS spectra of the Ca-rich bodywas distinct from both coccolith calcite and the embedding resin, suggestingthat the body does not contain significant amounts of calcium carbonate (Fig. 4c). Interestingly, the spectrum of the body showed asmall peak at 288.2 eV, which has been previously associated with amidecarbonyl bonds and suggests the presence of proteins26. To oursurprise, the EDX analysis revealed the Ca-rich bodies to contain very highamounts of P in addition to Ca and minor amounts of other elements (Fig. 4d). Among these elements was magnesium, an importanttrace element in coccolith calcite, whose amount relative to calcium is used toinfer past climatic conditions5. The excess of P over Ca in theCa-rich body (Supplementary Table1) suggests that Ca is bound by phosphate-rich macromolecules. Becausethe amount of P exceeds the amount of carbon, the most plausible candidates arenot phosphorylated biomolecules but rather polyphosphates, which have beenproposed to play a role in CaCO3 biomineralization27and were discovered already in the non-calcifying relative of E. huxleyi,Pavlova ennorea sp. nov.28. In E. huxleyipolyphosphates may be synthesized by the enzyme polyphosphate polymerase (JGIID406855)29.

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