Selective Uptake of Alkaline Earth Metals by Cyanobacteria Forming Intracellular Carbonates

Abstract

The uptakes of calcium (Ca), strontium (Sr), and barium (Ba) by two cyanobacterial strains, Cyanothece sp. PCC7425 and Gloeomargarita lithophora, both forming intracellular carbonates, were investigated in laboratory cultures. In the culture medium BG-11 amended with 250 μM Ca and 50 or 250 μM Sr and Ba, G. lithophora accumulated first Ba, then Sr, and finally Ca. Sr and Ba were completely accumulated by G. lithophora cells at rates between 0.02 and 0.10 fmol h cell and down to extracellular concentrations below the detection limits of inductively coupled plasma atomic emission spectroscopy. Accumulation of Sr and Ba did not affect the growth rate of the strain. This sequential accumulation occurred mostly intracellularly within polyphosphate and carbonate granules and resulted in the formation of core-shell structures in carbonates. In contrast, Cyanothece sp. PCC7425 showed neither a preferential accumulation of heavier alkaline earth metals nor core-shell structures in the carbonates. This indicated that fractionation between alkaline earth metals was not inherent to intracellularly calcifying cyanobacteria but was likely a genetically based trait of G. lithophora. Overall, the capability of G. lithophora to sequester preferentially Sr and Ba at high rates may be of considerable interest for designing new remediation strategies and better understanding the geochemical cycles of these elements.

Evidence of high Ca uptake by cyanobacteria forming intracellular CaCO3 and impact on their growth

“…Several previous studies have assessed cell Ca uptake by measuring the temporal changes of dissolved extracellular Ca 2+ concentration (Blondeau, Benzerara, et al., ; Cam et al., ; Singh & Mishra, ). Yet, changes in dissolved Ca concentrations can a priori be due to (a) extracellular precipitation of Ca‐containing mineral phases, (b) adsorption at the cell surfaces and/or by surface EPS, and/or (c) Ca uptake within cells.…”

“…Several previous studies have assessed cell Ca uptake by measuring the temporal changes of dissolved extracellular Ca 2+ concentration Cam et al, 2016;Singh & Mishra, 2014 Ca uptake systematically higher than other cyanobacteria.…”

Amorphous Calcium Carbonate Granules Form Within an Intracellular Compartment in Calcifying Cyanobacteria

“…This discovery was particularly surprising since cyanobacterium-mediated carbonatogenesis was before then thought to be exclusively extracellular (e.g., Riding, 2006 ; Dittrich and Sibler, 2010 ). Moreover, intracellular biomineralization of carbonates by G. lithophora was shown to be associated with the capability to strongly accumulate Sr and Ba offering some potential for remediating pollutions by these elements ( Cam et al, 2016 ; Blondeau et al, 2018 ). Finally, G. lithophora was recently proposed as the present-day closest cultured relative of primary plastids ( Ponce-Toledo et al, 2017 ), questioning the capability of their common ancestor to form intracellular CaCO 3 .…”

Precipitation of calcium carbonate mineral induced by viral lysis of cyanobacteria: evidence from laboratory experiments

“…In contrast, diverse cyanobacterial taxa have recently been shown to form amorphous calcium carbonate (ACC) minerals intracellularly, which have diameters of several hundreds of nanometers (Couradeau et al, 2012;Benzerara et al, 2014). The intracellular carbonate makes the mechanisms involved in calcification more confusing (Cam et al, 2015(Cam et al, , 2018Li et al, 2016). Thus, new pathways, in which some biological processes alter the carbonate system, are important to evaluate.…”