Until now, descriptions of intracellular biomineralization of amorphous inclusions involving alkaline‐earth metal (AEM) carbonates other than calcium have been confined exclusively to cyanobacteria (Couradeau et al., 2012). Here, we report the first evidence of the presence of intracellular amorphous granules of AEM carbonates (calcium, strontium, and barium) in unicellular eukaryotes. These inclusions, which we have named micropearls, show concentric and oscillatory zoning on a nanometric scale. They are widespread in certain eukaryote phytoplankters of Lake Geneva (Switzerland) and represent a previously unknown type of non‐skeletal biomineralization, revealing an unexpected pathway in the geochemical cycle of AEMs. We have identified Tetraselmis cf. cordiformis (Chlorophyta, Prasinophyceae) as being responsible for the formation of one micropearl type containing strontium ([Ca,Sr]CO₃), which we also found in a cultured strain of Tetraselmis cordiformis. A different flagellated eukaryotic cell forms barium‐rich micropearls [(Ca,Ba)CO₃]. The strontium and barium concentrations of both micropearl types are extremely high compared with the undersaturated water of Lake Geneva (the Ba/Ca ratio of the micropearls is up to 800,000 times higher than in the water). This can only be explained by a high biological pre‐concentration of these elements. The particular characteristics of the micropearls, along with the presence of organic sulfur‐containing compounds—associated with and surrounding the micropearls—strongly suggest the existence of a yet‐unreported intracellular biomineralization pathway in eukaryotic micro‐organisms.

中文翻译：

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细胞内无定形碳酸盐揭示了真核生物中新的生物矿化过程。

到目前为止，有关除钙以外的碱土金属（AEM）碳酸盐的无定形夹杂物的细胞内生物矿化的描述仅限于蓝细菌（Couradeau et al。，2012）。在这里，我们报告的单细胞真核生物中存在AEM碳酸盐（钙，锶和钡）的细胞内无定形颗粒的第一个证据。这些被我们称为微珍珠的包裹体，在纳米尺度上显示出同心和振荡带。它们广泛存在于日内瓦湖（瑞士）的某些真核生物浮游植物中，代表了以前未知的非骨骼生物矿化类型，揭示了AEMs地球化学循环中的意外途径。我们确定了Tetraselmiscf。堇菜（绿藻科）（Chlorophyta，Prasinophyceae）负责形成一种含锶（[Ca，Sr] CO ₃）的微珍珠类型，我们也在培养的四叶草（Tetraselmis cordiformis）菌株中发现了这种微珍珠。不同的鞭毛真核细胞形成富含钡的微珍珠[（Ca，Ba）CO ₃]。与日内瓦湖的欠饱和水相比，两种微珍珠的锶和钡的浓度都非常高（微珍珠的Ba / Ca比值高达水的800,000倍）。这只能通过这些元素的高生物预浓缩来解释。微珠的特殊特征，以及与微珠相关并围绕微珠的有机含硫化合物的存在，强烈表明真核微生物中存在尚未报道的细胞内生物矿化途径。