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Biomineralization of intracelllar amorphous calcium carbonates (ACC) by bacteria: molecular mechanisms, evolutionary history and environmental significance
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International audience. The biomineralization of amorphous calcium carbonates (ACC) has been abundantly documented in eukaryotes. ACC appears as a key precursor phase in the formation of most carbonate biominerals and its solubility and chemistry control, to a great extent, biomineralization processes and the physico-chemical properties of the biomineral endproducts. Interestingly, biomineralization of intracellular ACC has been reported in an increasing number of prokaryotes: environmentally and phylogenetically diverse cyanobacteria; the gammaproteobacterium Achromatium; a newly described magnetotactic bacterium affiliated to the Alphaproteobacteria. It has been proposed that these bacteria may have a significant impact on local geochemical cycles of alkaline earth metals and carbon. Moreover, at least some of these bacteria may serve for the development of new bioremediation routes of radioactive earth alkaline metals such as Ra or 90Sr. Yet, the molecular mechanisms involved in the bacterial biomineralization of ACC remain poorly known. Here, I will present the discovery of a new gene specifically involved in the biomineralization of ACC in cyanobacteria. The function of this gene will be discussed. Moreover, I will show how it allows an efficient further detection of the phylogenetic diversity of this biomineralization process within cyanobacteria as well as inferences about its evolutionary history. Last, I will analyze and speculate about the potential relationships between ACC biomineralization in these different organisms.
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