Institut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC), UMR CNRS 7590, Muséum National d'Histoire Naturelle, IRD UMR 206, Sorbonne Universités, UPMC Univ Paris 6, Paris, France.
Laboratoire de Réactivité de Surface (LRS), UMR CNRS 7197, Sorbonne Universités, UPMC Univ Paris 6, Paris, France.
Geobiology. 2018 Jan;16(1):49-61. doi: 10.1111/gbi.12261. Epub 2017 Oct 26.
Cyanobacteria have long been thought to induce the formation of Ca-carbonates as secondary by-products of their metabolic activity, by shifting the chemical composition of their extracellular environment to conditions favoring mineral precipitation. Some cyanobacterial species forming Ca-carbonates intracellularly were recently discovered. However, the environmental conditions under which this intracellular biomineralization process can occur and the impact of cyanobacterial species forming Ca-carbonates intracellularly on extracellular carbonatogenesis are not known. Here, we show that these cyanobacteria can form Ca-carbonates intracellularly while growing in extracellular solutions undersaturated with respect to all Ca-carbonate phases, that is, conditions thermodynamically unfavorable to mineral precipitation. This shows that intracellular Ca-carbonate biomineralization is an active process; that is, it costs energy provided by the cells. The cost of energy may be due to the active accumulation of Ca intracellularly. Moreover, unlike cyanobacterial strains that have been usually considered before by studies on Ca-carbonate biomineralization, cyanobacteria forming intracellular carbonates may slow down or hamper extracellular carbonatogenesis, by decreasing the saturation index of their extracellular solution following the buffering of the concentration of extracellular calcium to low levels.
蓝藻一直被认为可以通过改变其细胞外环境的化学成分，使其有利于矿物沉淀，从而作为代谢活动的次要副产物诱导 Ca 碳化物的形成。最近发现了一些在细胞内形成 Ca 碳化物的蓝藻物种。然而，目前尚不清楚这种细胞内生物矿化过程发生的环境条件以及在细胞内形成 Ca 碳化物的蓝藻物种对细胞外碳酸盐形成的影响。在这里，我们表明，这些蓝藻可以在细胞外溶液中不饱和的所有 Ca 碳酸盐相的情况下在细胞内形成 Ca 碳化物，也就是说，在热力学上不利于矿物沉淀的条件下。这表明细胞内 Ca 碳化物生物矿化是一个主动过程；也就是说，它需要细胞提供的能量。能量的成本可能是由于 Ca 在内质网中的主动积累。此外，与以前关于 Ca 碳化物生物矿化的研究中通常考虑的蓝藻菌株不同，形成细胞内碳酸盐的蓝藻可能会通过缓冲细胞外钙浓度至低水平来降低细胞外溶液的饱和度指数，从而减缓或阻碍细胞外碳酸盐的形成。
