Dissimilatory iron-reducing bacteria (DIRB) oxidize organic matter or hydrogen and reduce ferric iron to form Fe(II)-bearing minerals, such as magnetite and siderite. However, compared with magnetite, which was extensively studied, the mineralization process and mechanisms of siderite remain unclear. Here, with the combination of advanced electron microscopy and synchrotron-based scanning transmission X-ray microscopy (STXM) approaches, we studied in detail the morphological, structural, and chemical features of biogenic siderite via a growth experiment with Shewanella oneidensis MR-4. Results showed that along with the growth of cells, Fe(II) ions were increasingly released into solution and reacted with CO₃^2– to form micrometer-sized siderite minerals with spindle, rod, peanut, dumbbell, and sphere shapes. They are composed of many single-crystal siderite plates that are fanned out from the center of the particles. Additionally, STXM revealed Fh and organic molecules inside siderite. This suggests that the siderite crystals might assemble around a Fh-organic molecule core and then continue to grow radially. This study illustrates the biomineralization and assembly of siderite by a successive multistep growth process induced by DIRB, also provides evidences that the distinctive shapes and the presence of organic molecules inside might be morphological and chemical features for biogenic siderite.

中文翻译：

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铁还原菌产生的菱铁矿的形态、微观结构和原位化学特征

异化铁还原菌 (DIRB) 氧化有机物或氢气并还原三价铁，形成含 Fe(II) 的矿物，例如磁铁矿和菱铁矿。然而，与广泛研究的磁铁矿相比，菱铁矿的成矿过程和机制仍不清楚。在这里，我们结合先进的电子显微镜和基于同步加速器的扫描透射 X 射线显微镜 (STXM) 方法，通过Shewanella oneidensis MR-4 的生长实验详细研究了生物菱铁矿的形态、结构和化学特征。结果表明，随着细胞的生长，Fe(II)离子逐渐释放到溶液中并与CO ₃ ^2–反应形成微米级菱铁矿矿物，其形状为纺锤形、棒形、花生形、哑铃形和球形。它们由许多从颗粒中心呈扇形展开的单晶菱铁矿板组成。此外，STXM 还揭示了菱铁矿内部的 Fh 和有机分子。这表明菱铁矿晶体可能聚集在 Fh 有机分子核心周围，然后继续径向生长。这项研究说明了 DIRB 诱导的连续多步生长过程对菱铁矿的生物矿化和组装，也提供了证据表明独特的形状和内部有机分子的存在可能是生物菱铁矿的形态和化学特征。