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Impact of the cyanobacterium Gloeomargarita lithophora on the geochemical cycles of Sr and Ba

Abstract : The cyanobacterium Gloeomargarita lithophora forms intracellular amorphous calcium carbonates and has been recently shown to accumulate Ca, Sr and Ba at a high level with a preference for Ba > Sr > Ca. This is of interest to the design of bioremediation strategies for Sr and/or Ba pollutions in aquatic systems. However, this preference has so far been evidenced at high dissolved Sr and Ba concentrations only, i. e. conditions rarely encountered in the environment. Here, we followed the uptake of alkaline earth metals (Mg, Ca, Sr and Ba) by G. lithophora in alkaline solutions with more environmentally-relevant, low Sr and Ba concentrations. Two settings were analyzed: 1) batch cultures in which alkaline earth metals were added only at the beginning; 2) cultures supplemented continuously with fragments of alkaline earth element-containing carbonate microbialites. The growth of G. lithophora was higher in the presence of microbialites, suggesting that some limiting elements, possibly P and/or Ca, were supplied by their dissolution. In the two settings, the concentration of dissolved Ca was in the micromolar range, while it was more than three orders of magnitude lower for Ba and Sr. In cultures with microbialite fragments, these low Sr and Ba concentrations resulted from an input by aragonite dissolution balanced by high Sr and Ba uptake by the cyanobacterial cells with high affinity. Thereby, the continuous supply of alkaline earth metals by microbialite dissolution increased the Sr and Ba content of the cyanobacterial intracellular carbonates over time. G. lithophora incorporated preferentially Ba and Sr over Ca even at very low Ba and Sr concentrations and despite the presence of Ca at a much higher concentration. Overall, this shows the capability of G. lithophora to impact the geochemical cycles of Sr and Ba by buffering dissolved Sr/Ca and Ba/Ca ratios at low levels.
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Marine Blondeau, Karim Benzerara, Céline Férard, Jean-Michel Guigner, Melanie Poinsot, et al.. Impact of the cyanobacterium Gloeomargarita lithophora on the geochemical cycles of Sr and Ba. Chemical Geology, Elsevier, 2018, 483, pp.88-97. ⟨10.1016/j.chemgeo.2018.02.029⟩. ⟨insu-02892129⟩



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