Sequestration of Radionuclides Radium-226 and Strontium-90 by Cyanobacteria Forming Intracellular Calcium Carbonates

Neha Mehta (1) , Karim Benzerara (2) , Benjamin Kocar (1) , Virginie Chapon (3, 4)

1 MIT - Massachusetts Institute of Technology
2 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie
3 BIAM - Institut de Biosciences et Biotechnologies d'Aix-Marseille (ex-IBEB)
4 IPM - Interactions Protéine Métal

$^{226}$Ra is a naturally occurring radionuclide with a half-life of 1600 y. In contrast, $^{90}$Sr is a radionuclide of sole anthropogenic origin, produced by nuclear fission reactions and has a half-life of 29 y; each of these radionuclides poses potential threats to 16 human and ecosystem health. Here, the cyanobacterium $G.\ lithophora$, capable of forming intracellular amorphous calcium carbonate inclusions, was investigated for its ability to uptake $^{226}$ Ra and $^{90}$Sr. In BG-11 medium, $G.\ lithophora$ accumulated 3.9 $\mu$g g$^{-1}$ $^{226}$Ra within 144 h and 47.9 ng g$^{-1}$ $^{90}$Sr within 1 h, corresponding to $\sim$99% removal of trace radionuclides. The presence of high concentration Ca$^{2+}$ in the background media solution did not inhibit $^{90}$Sr and $^{226}$Ra uptake by $G.\ lithophora$. In contrast, dead biomass of $G.\ lithophora$ accumulated 0.8 $\mu$g g$^{-1}$ $^{226}$Ra and 8.87 ng g$^{-1}$ $^{90}$Sr. Moreover, Synechocystis, a non-biomineralizing cyanobacteria removed only 14% and 25% of $^{226}$Ra and $^{90}$Sr, respectively. This suggested that sequestration of $^{90}$Sr and $^{226}$Ra was not intrinsic to all cyanobacteria but was likely a specific biological trait of $G.\ lithophora$ related to the formation of intracellular amorphous Ca-carbonates. The unique ability of $G.\ lithophora$ to uptake $^{90}$Sr and $^{226}$Ra at high rates makes it an attractive candidate for further studies involving bioremediation of these radionuclides.

Domaines: Sciences du Vivant [q-bio]

Neha Mehta, Karim Benzerara, Benjamin Kocar, Virginie Chapon. Sequestration of Radionuclides Radium-226 and Strontium-90 by Cyanobacteria Forming Intracellular Calcium Carbonates. Environmental Science and Technology, 2019, 53 (21), pp.12639-12647. ⟨10.1021/acs.est.9b03982⟩. ⟨cea-02374665⟩