In-vitro synthesis of amorphous Mg-, Ca-, Sr- and Ba-carbonates:

what do we learn about intracellular calcification by cyanobacteria?

Nithavong Cam1, 2 Jean-François Lambert1, Karim Benzerara2,

Thomas Georgelin1, Maguy Jaber

1 Laboratoire de Réactivité des Surfaces, UMR 7197, CNRS & UPMC2 Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, UMR 7590, CNRS & UMPC, Muséum National d’Histoire Naturelle, IRD UMR 206

2

Cyanobacteria and mineralization

Photosynthetic bacteria

Riding R. (2006) Geobiology (4); 299:316

6 CO2 + 6 H2O → C6H12O6 + 6 O2

used to be considered as exclusively extracellular

important mineralization activity

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Some cyanobacteria form intracellular carbonates

K. Benzerara et al. (2014) PNAS (111); 10933:10938

Cyanothece sp. PCC 7425

Synechococcus sp. PCC 63121 µm

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Particularities of intracellular carbonates

Inclusions Ø:75-500 nm

Amorphous

E. Couradeau et al. (2012) Science (336); 6080, 459:462

Enriched in Sr and Ba

= 86

= 1370

Mg0.18Ca0.53Sr0.08Ba0.21CO3

Sr/Ca solidSr/Ca solution

Ba/Ca solidBa/Ca solution

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Some properties of calcium carbonates

Partitioning 0.021 (X=Sr)0.012 (X=Ba)

Amorphous (ACC)

How does the cell stabilize the amorphous phase?

Calcite Aragonite

Dietzel M. et al.(2004)Tesoriero A. J. and Pankow J. F. (1996)

1.19 (X=Sr)1.5 (X=Ba)

X/Ca solid X/Ca solution

?

Where does come from the partitioning?

25 °C

3.31 x10-9 M2 4.57 x10-9 M2

M. Kellermeier et al. (2014)

2.32 x10-8 M2 SolubilityPlummer L. N. and Busenberg E. (1982)< <

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CO32-Mg2+

Sr2+Ca2+

Ba2+

+ CO32- Abiotic carbonates

[Mg2+]= 10 mM [Ca2+]= 5.3 mM [Sr2+]= 0.8 mM [Ba2+]= 2.1 mM

Same Sr/Ca and Ba/Ca ratios as observed in cyanobacteria carbonates

Initial pH = 10.6

SIACC = 1.803SI = log (IAP/Ks)

[CO32-]= 10 mM

Procedure for carbonate precipitation

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Similarities:

- size- poor crystallinity- composition

Elemental ratios in precipitates are same as in the solution

Mg0.16Ca0.51Sr0.05Ba0.28CO3Ø ≈ 200 nm

Poorly crystalline

Cam N. et al. (2015) Geochimica et Cosmochimica Acta (161); 36:49.

Abiotic carbonates like bacterial ones

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Association of Mg with Sr or Ba helps amorphous phase stability

without Mg

without Sr without Ba

without Sr and Ba

Calcite

Poorly crystalline

Monohydrocalcite

SEM SEM

TEM TEM

Poorly crystalline

Substituants effect in carbonates precipitation

Cam N. et al. (2015) Geochimica et Cosmochimica Acta (161); 36:49.

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H2O MgCO3 -> CO2+ MgO CaCO3 -> CO2+ CaO

~ 1 H2O per 1 CO3 unitAs observed in biotic and abiotic ACC L.Brečević and A.E. Nielsen (1989)

For further in abiotic ACC characterization

Mg0.16Ca0.51Sr0.05Ba0.28CO3·1.03H2O

Thermogravimetric analysis

Cam N. et al. (2015) Geochimica et Cosmochimica Acta (161); 36:49.

CO2

DTG

Heat flow

(derivative of the weight loss)

CO2

DTG

Heat flow

(derivative of the weight loss)

325°C 375°C

Exothermic event = Crystallization

Calcite

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XRD

Thermogravimetric analysis

For further in abiotic ACC characterization

Cam N. et al. (2015) Geochimica et Cosmochimica Acta (161); 36:49.

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Reproduce similar carbonates in an abiotic way is possible

Conclusions

no partitioning between Ca, Sr and Ba

≈ 1Sr/Ca solidSr/Ca solution

Ba/Ca solid Ba/Ca solution ≈ 1

Amorphous calcium carbonate

enrichment in Sr and Ba inside the cells

carbonates formation solution has same elemental ratios as the minerals

– size– poor crystallinity– composition

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– pH = 10.64

– [Ca] = 5.3 mM

– [inorganic carbon] = 10 mM

About precipitation solution composition

Known chemistry of cyanobacteria intracellular medium is very different

– pH < 7.9

– [Ca]< 2.6µM

– [inorganic carbon] < 30 mM

Cyanobacteria intracellular medium

A. L. Barrán-Berdón et al. (2011)

M. R. Badger and T. J. Andrews (1982)

H.-B.Jiang et al. (2013)

SIACC = -2.225 no precipitation SIACC = 1.803

what we know about cyanobacteria intracellular composition can not explain the precipitation of calcium carbonate

Abiotic synthesis medium

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Thank you for attention

This work was supported by French state funds managed by the ANR within the Investissements d'Avenir programme under reference ANR-11-IDEX-0004-02, and more specifically within the framework of the Cluster of Excellence MATISSE

G. Morin, F. Skouri-Panet and M. Poinsot (IMPMC)Acknowledgment:

K.Benzerara was supported by ERC grant (Calcyan)