Cyanobacteria Accumulate Radium (Ra-226) within Intracellular Amorphous Calcium Carbonate Inclusions

Recently, the cyanobacteriumGleomargarita lith-ophorawas shown to be associated with the capability to stronglyaccumulate Ra-226 (radioactive pollutant) and was suggested as anovel bioremediation strategy for the removal of Ra-226. Thebioaccumulation of Ra-226 was suggested to be linked with theability ofG. lithophorato form intracellular amorphous calciumcarbonate mineral inclusions (iACC). However, this claim reliedon indirect evidence, and the fate of (intracellularly) sequestered Ra-226 remains unresolved because of the limited spatial resolutionof conventional analytical instrumentation. Here, using high-resolution nanoscale secondary-ion mass spectrometry (Nano-SIMS), we show that sequestered Ra-226 is primarily associated withiACC and to a lesser degree within polyphosphate inclusions,which are also present inG. lithophora. Moreover, we show thatG.lithophoraaccumulates Ra-226 efficiently in the presence ofcompeting cations such as barium and strontium (frequentlypresent in Ra-bearing effluents). Our results offer fundamentalinsights into the interactions between microorganisms and Ra-226, benefit the future development of efficient Ra-226 bioremediationstrategies, and present a new frontier in the mapping of ultratrace elements in microbial samples using NanoSIMS.