Molecular mechanisms of intracellular calcium carbonate biomineralization

The reason why some cyanobacteria form intracellular CaCO₃ while others do not, remains to be determined. We synthesized abiotically amorphous carbonates with a chemical composition, a morphology and a size similar to the carbonates formed by Ca. G. lithophora (Cam et al., 2015). However, this was performed in solutions highly supersaturated with carbonate phases, while it is commonly assumed that cyanobacterial cells regulate their cytoplasmic chemical composition below Ca-carbonate saturation, with a Ca concentration around 100 nM, a near-neutral pH and a high inorganic carbon content around 30 mM. Cyanobacteria forming intracellular CaCO₃ can contain high Ca contents, up to 3.5 fmol per cell (Li et al., 2016). We now point out that a diverging homeostasis of Ca might be one crucial explanation to intracellular calcification (De Wever, in prep). Very recently, in collaboration with Isabelle Callebaut and Elodie Duprat at IMPMC, we have conducted comparative genomics analyses which will provide further insight on the molecular processes involved specifically in intracellular CaCO₃ biomineralization.