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

226Ra is a naturally occurring radionuclide with a half-life of 1600 years. In contrast, 90Sr is a radionuclide of sole anthropogenic origin, produced by nuclear fission reactions and has a half-life of 29 years; each of these radionuclides poses potential threats to human and ecosystem health. Here, the cyanobacterium Gloeomargarita lithophora, capable of forming intracellular amorphous calcium carbonate inclusions, was investigated for its ability to uptake 226Ra and 90Sr. In BG-11 medium, G. lithophora accumulated 3.9 μg g-1 of 226Ra within 144 h and 47.9 ng g-1 of 90Sr within 1 h, corresponding to ∼99% removal of trace radionuclides. The presence of high-concentration Ca2+ in the background media solution did not inhibit 90Sr and 226Ra uptake by G. lithophora. In contrast, dead biomass of G. lithophora accumulated 0.8 μg g-1 of 226Ra and 8.87 ng g-1 of 90Sr. Moreover, Synechocystis, a nonbiomineralizing cyanobacteria, removed only 14 and 25% of 226Ra and 90Sr, respectively. This suggested that sequestration of 90Sr and 226Ra 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 90Sr and 226Ra at high rates makes it an attractive candidate for further studies involving bioremediation of these radionuclides.