Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, UMR CNRS 7590, Sorbonne Université, Muséum National d'Histoire Naturelle, Paris, France.
Collection des Cyanobactéries, Institut Pasteur, Paris Cedex 15, France.
Geobiology. 2019 Nov;17(6):676-690. doi: 10.1111/gbi.12358. Epub 2019 Jul 26.
Several species of cyanobacteria biomineralizing intracellular amorphous calcium carbonates (ACC) were recently discovered. However, the mechanisms involved in this biomineralization process and the determinants discriminating species forming intracellular ACC from those not forming intracellular ACC remain unknown. Recently, it was hypothesized that the intensity of Ca uptake (i.e., how much Ca was scavenged from the extracellular solution) might be a major parameter controlling the capability of a cyanobacterium to form intracellular ACC. Here, we tested this hypothesis by systematically measuring the Ca uptake by a set of 52 cyanobacterial strains cultured in the same growth medium. The results evidenced a dichotomy among cyanobacteria regarding Ca sequestration capabilities, with all strains forming intracellular ACC incorporating significantly more calcium than strains not forming ACC. Moreover, Ca provided at a concentration of 50 μM in BG-11 was shown to be limiting for the growth of some of the strains forming intracellular ACC, suggesting an overlooked quantitative role of Ca for these strains. All cyanobacteria forming intracellular ACC contained at least one gene coding for a mechanosensitive channel, which might be involved in Ca influx, as well as at least one gene coding for a Ca /H exchanger and membrane proteins of the UPF0016 family, which might be involved in active Ca transport either from the cytosol to the extracellular solution or the cytosol toward an intracellular compartment. Overall, massive Ca sequestration may have an indirect role by allowing the formation of intracellular ACC. The latter may be beneficial to the growth of the cells as a storage of inorganic C and/or a buffer of intracellular pH. Moreover, high Ca scavenging by cyanobacteria biomineralizing intracellular ACC, a trait shared with endolithic cyanobacteria, suggests that these cyanobacteria should be considered as potentially significant geochemical reservoirs of Ca.
最近发现了几种能够生物矿化细胞内无定形碳酸钙（ACC）的蓝细菌。然而，该生物矿化过程所涉及的机制以及区分形成细胞内 ACC 的物种和不形成细胞内 ACC 的物种的决定因素仍不清楚。最近，有人假设 Ca 摄取强度（即从细胞外溶液中摄取了多少 Ca）可能是控制蓝细菌形成细胞内 ACC 的能力的一个主要参数。在这里，我们通过系统地测量在相同生长培养基中培养的 52 株蓝细菌的 Ca 摄取量来测试这一假设。结果表明，在 Ca 螯合能力方面，蓝细菌存在二分法，所有形成细胞内 ACC 的菌株掺入的 Ca 显著多于不形成 ACC 的菌株。此外，在 BG-11 中提供 50 μM 的 Ca 被证明会限制一些形成细胞内 ACC 的菌株的生长，这表明 Ca 对这些菌株的作用被忽视了。所有形成细胞内 ACC 的蓝细菌都至少含有一个编码机械敏感通道的基因，该基因可能参与 Ca 内流，以及至少一个编码 Ca/H 交换器和 UPF0016 家族膜蛋白的基因，该基因可能参与主动 Ca 运输，无论是从细胞质到细胞外溶液还是细胞质到细胞内隔室。总的来说，大量的 Ca 螯合可能通过允许形成细胞内 ACC 而发挥间接作用。后者可能对细胞的生长有益，因为它可以作为无机 C 的储存库和/或细胞内 pH 的缓冲剂。此外，能够生物矿化细胞内 ACC 的蓝细菌会大量摄取 Ca，这一特征与内生蓝细菌共享，这表明这些蓝细菌应该被视为潜在的重要 Ca 地球化学储库。
