Abstract The origin of dolomite has long puzzled geologists. It has recently been documented that sulfate-reducing bacteria (SRB) are capable of catalyzing the formation of protodolomite, a previously proposed precursor of ordered sedimentary dolomite. However, the catalytic mechanism of SRB remains incompletely understood. This experimental study is aimed at probing the effect of capsule extracellular polymeric substances (capsule EPS) from SRB on the crystallization of protodolomite in vivo. The capsule EPS tested herein was isolated from a protodolomite-mediating SRB, Desulfotomaculum ruminis, and added into a solution wherein the degree of oversaturation was close to the growth medium of D. ruminis at stationary phase. The solid products were characterized with X-ray diffraction (XRD), Raman spectroscopy and, scanning and transmission electron microscopy (SEM and TEM). Our results indicated that aragonite emerged in the reactors without capsule EPS, while Ca-Mg carbonates (Mg-calcite and protodolomite) were produced in the systems amended with capsule EPS. The incorporation amount of Mg2+ in Ca-Mg carbonates was enhanced with the increasing concentration of capsule EPS. The predominant occurrence of protodolomite was found in the reactor with 140 mg/L capsule EPS. These resulting protodolomites were spherical in shape, and composed of numerous nano-particles. The catalytic influence of capsule EPS on the precipitation of protodolomite might be attributed to their strong Mg2+ binding capacity, potentially diminishing Mg-hydration, which is a potent inhibitor of protodolomite crystallization. The results of Fourier transformation infrared (FT-IR) spectra showed that Mg2+ was bonded with carboxyl and hydroxyl groups on capsule EPS. This inferred adsorption capacity of capsule EPS was also supported by new calculations of complexation chemistry between Mg-H2O complex and organic compounds present in capsule EPS.

中文翻译：

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硫酸盐还原菌促进原白云岩的沉淀：荚膜胞外聚合物的作用

摘要 白云岩的成因长期以来一直困扰着地质学家。最近有记录表明，硫酸盐还原菌 (SRB) 能够催化原白云岩的形成，原白云岩是先前提出的有序沉积白云岩的前体。然而，SRB 的催化机制仍未完全了解。本实验研究旨在探讨来自SRB的胶囊胞外聚合物（胶囊EPS）对体内原白云石结晶的影响。将本文测试的胶囊EPS从原白云石介导的SRB、Desulfotomaculum ruminis中分离，并加入到溶液中，其中过饱和度接近静止期D. ruminis的生长培养基。固体产物用 X 射线衍射 (XRD)、拉曼光谱和，扫描和透射电子显微镜（SEM 和 TEM）。我们的结果表明文石出现在没有胶囊 EPS 的反应器中，而 Ca-Mg 碳酸盐（Mg-方解石和原白云石）在用胶囊 EPS 修正的系统中产生。随着胶囊EPS浓度的增加，Ca-Mg碳酸盐中Mg2+的掺入量增加。在具有 140 mg/L 胶囊 EPS 的反应器中发现原白云岩的主要存在。这些生成的原白云岩呈球形，由无数纳米颗粒组成。胶囊 EPS 对原白云石沉淀的催化作用可能归因于它们强大的 Mg2+ 结合能力，可能会减少 Mg 水合，而镁水合是原白云石结晶的有效抑制剂。傅里叶变换红外 (FT-IR) 光谱结果表明，Mg2+ 与胶囊 EPS 上的羧基和羟基键合。这种推断的胶囊 EPS 吸附能力也得到了 Mg-H2O 复合物与胶囊 EPS 中存在的有机化合物之间络合化学的新计算的支持。