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

Speciation of cellular calcium during the early stages of coccolith formationin E. huxleyi.(a) Time-resolved evolution of the XANES spectra (black) of cellsinduced to form calcite and of the calculated fits (orange) using linearcombinations of three reference standards (coccolith calcite, free calciumions and amorphous CaCO3). (b) Ca K-edge XANES spectra ofcalcium reference standards and of E. huxleyi cells enclosed by asphere of coccoliths (C cells). Free calcium ions were represented by10 mM CaCl2 solution. The spectrum of amorphous calciumphosphate is courtesy of Diane Eichert, Elettra synchrotron, Trieste,Italy47. The spectrum of C cells showed thecharacteristic feature of calcite and was used instead of synthetic calcitefor fitting the spectra of induced cells. (c) Relative contributionof the calcium references to the three component fits shown in a.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Speciation of cellular calcium during the early stages of coccolith formationin E. huxleyi.(a) Time-resolved evolution of the XANES spectra (black) of cellsinduced to form calcite and of the calculated fits (orange) using linearcombinations of three reference standards (coccolith calcite, free calciumions and amorphous CaCO3). (b) Ca K-edge XANES spectra ofcalcium reference standards and of E. huxleyi cells enclosed by asphere of coccoliths (C cells). Free calcium ions were represented by10 mM CaCl2 solution. The spectrum of amorphous calciumphosphate is courtesy of Diane Eichert, Elettra synchrotron, Trieste,Italy47. The spectrum of C cells showed thecharacteristic feature of calcite and was used instead of synthetic calcitefor fitting the spectra of induced cells. (c) Relative contributionof the calcium references to the three component fits shown in a.

Mentions: Our initial investigation of E. huxleyi for possible amorphous precursorphases of coccolith calcite involved X-ray absorption near-edge structure(XANES) spectroscopy. Cryogenic XANES is uniquely suited to discriminate calciumspecies in mixtures and played a pivotal role in the discovery of solubleinorganic phases during the formation of crystalline biominerals1516. To follow intracellular Ca during the deposition of freshcoccolith calcite, we raised ‘calcite-free' E. huxleyi cells(Supplementary Fig. 1),induced calcite formation by adding Ca2+ to the medium andcryo-preserved cells at 10-min intervals up to 30 min, which is whencalcite crystals of status nascendi coccoliths are detectable bycross-polarized light microscopy (Supplementary Fig. 1b). The XANES spectrum of cells before induction(0 min) had a small shoulder at 4,060 eV, which increased overtime and is indicative for calcite formation (Fig. 1a). Wefitted the spectra of the induced cells using linear combinations of severalreference spectra (Fig. 1b). The differences between thedifferent linear combinations were minor, even though the best fits wereobtained when using amorphous calcium carbonate (ACC) in addition toCaCl2 solution and calcite (Fig. 1a; seeSupplementary Fig. 2a,b forfits with other reference spectra). This suggests that yet unidentifiedamorphous Ca phases are a significant fraction of intracellular calcium at alltime points (Fig. 1c).


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)

Speciation of cellular calcium during the early stages of coccolith formationin E. huxleyi.(a) Time-resolved evolution of the XANES spectra (black) of cellsinduced to form calcite and of the calculated fits (orange) using linearcombinations of three reference standards (coccolith calcite, free calciumions and amorphous CaCO3). (b) Ca K-edge XANES spectra ofcalcium reference standards and of E. huxleyi cells enclosed by asphere of coccoliths (C cells). Free calcium ions were represented by10 mM CaCl2 solution. The spectrum of amorphous calciumphosphate is courtesy of Diane Eichert, Elettra synchrotron, Trieste,Italy47. The spectrum of C cells showed thecharacteristic feature of calcite and was used instead of synthetic calcitefor fitting the spectra of induced cells. (c) Relative contributionof the calcium references to the three component fits shown in a.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Speciation of cellular calcium during the early stages of coccolith formationin E. huxleyi.(a) Time-resolved evolution of the XANES spectra (black) of cellsinduced to form calcite and of the calculated fits (orange) using linearcombinations of three reference standards (coccolith calcite, free calciumions and amorphous CaCO3). (b) Ca K-edge XANES spectra ofcalcium reference standards and of E. huxleyi cells enclosed by asphere of coccoliths (C cells). Free calcium ions were represented by10 mM CaCl2 solution. The spectrum of amorphous calciumphosphate is courtesy of Diane Eichert, Elettra synchrotron, Trieste,Italy47. The spectrum of C cells showed thecharacteristic feature of calcite and was used instead of synthetic calcitefor fitting the spectra of induced cells. (c) Relative contributionof the calcium references to the three component fits shown in a.
Mentions: Our initial investigation of E. huxleyi for possible amorphous precursorphases of coccolith calcite involved X-ray absorption near-edge structure(XANES) spectroscopy. Cryogenic XANES is uniquely suited to discriminate calciumspecies in mixtures and played a pivotal role in the discovery of solubleinorganic phases during the formation of crystalline biominerals1516. To follow intracellular Ca during the deposition of freshcoccolith calcite, we raised ‘calcite-free' E. huxleyi cells(Supplementary Fig. 1),induced calcite formation by adding Ca2+ to the medium andcryo-preserved cells at 10-min intervals up to 30 min, which is whencalcite crystals of status nascendi coccoliths are detectable bycross-polarized light microscopy (Supplementary Fig. 1b). The XANES spectrum of cells before induction(0 min) had a small shoulder at 4,060 eV, which increased overtime and is indicative for calcite formation (Fig. 1a). Wefitted the spectra of the induced cells using linear combinations of severalreference spectra (Fig. 1b). The differences between thedifferent linear combinations were minor, even though the best fits wereobtained when using amorphous calcium carbonate (ACC) in addition toCaCl2 solution and calcite (Fig. 1a; seeSupplementary Fig. 2a,b forfits with other reference spectra). This suggests that yet unidentifiedamorphous Ca phases are a significant fraction of intracellular calcium at alltime points (Fig. 1c).

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