Precipitation of amorphous CaCO3 (aragonite-like) by cyanobacteria: A STXM study of the influence of EPS on the nucleation process
Precipitation of amorphous CaCO3 (aragonite-like) by cyanobacteria: A STXM study of the influence of EPS on the nucleation process
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DOI：
10.1016/j.gca.2009.04.013
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发表时间：
2009-07-15
影响因子：
5
通讯作者：
Hitchcock, A. P.
中科院分区：
文献类型：
--
作者：
Obst, M.;Dynes, J. J.;Hitchcock, A. P.
文石型短程有序无定形或纳米晶碳酸钙(ACC)相是聚球藻PCC7942介导方解石沉淀的瞬时前驱物相。利用扫描透射式X射线显微镜(STXM)，在30 nm尺度上对吸附在胞外聚合物上的方解石、文石型CaCO3和钙与各种有机化合物等不同的钙物种进行了区分和绘制。无定形文石状CaCO3的成核发生在蓝藻产生的紧密结合的胞外聚合物(EPS)中，非常接近细胞壁。类文石CaCO3是ACC的一种，因为它既没有X射线衍射峰，也没有电子衍射峰。EPS中类文石CaCO3的沉淀量与细菌生长过程中的营养供应有关。在培养蓝藻的过程中，较高的营养浓度(N和P)会导致文石型CaCO3的沉淀量增加，而单位体积EPS中吸附的钙离子的量几乎与营养水平无关。在热力学稳定的方解石开始析出并失去过饱和度后，类文石CaCO3溶解，而Ca~(2+)仍吸附在EPS上，尽管浓度较低。在此基础上，建立了描述方解石在细小球藻表面成核的时空演化模型。在另一组STXM实验中，发现细胞表面沉淀的文石型CaCO3的数量取决于培养的生长阶段：处于指数生长期的细胞在EPS中吸附了大量的钙并介导了ACC的成核，而处于静止/死亡阶段的细胞既不吸附大量的钙离子，也不参与形成文石型CaCO3。结果表明，蓝藻沉淀X-射线无定形CaCO_3层可能是防止热力学稳定相方解石在其表面失控析出的一种保护机制。(C)2009爱思唯尔有限公司。保留所有权利。
An amorphous or nanocrystalline calcium carbonate (ACC) phase with aragonite-like short-range order was found to be a transient precursor phase of calcite precipitation mediated by cyanobacteria of the strain Synechococcus leopoliensis PCC 7942. Using scanning transmission X-ray microscopy (STXM), different Ca-species such as calcite, aragonite-like CaCO3, and Ca adsorbed on extracellular polymers were discriminated and mapped, together with various organic compounds, at the 30 nm-scale. The nucleation of the amorphous aragonite-like CaCO3 was found to take place within the tightly bound extracellular polymeric substances (EPS) produced by the cyanobacteria very close to the cell wall. The aragonite-like CaCO3 is a type of ACC since it did not show either X-ray or electron diffraction peaks. The amount of aragonite-like CaCO3 precipitated in the EPS was dependent on the nutrient supply during bacterial growth. Higher nutrient concentrations (both N and P) during the cultivation of the cyanobacteria resulted in higher amounts of precipitation of the aragonite-like CaCO3, whereas the amount of Ca2+ adsorbed per volume of EPS was almost independent of the nutrient level. After the onset of the precipitation of the thermodynamically stable calcite and loss of supersaturation the aragonite-like CaCO3 dissolved whereas Ca2+ remained sorbed to the EPS albeit at lower concentrations. Based on these observations a model describing the temporal and spatial evolution of calcite nucleation on the surface of S. leopoliensis was developed. In another set of STXM experiments the amount of aragonite-like CaCO3 precipitated on the cell surface was found to depend on the culture growth phase: cells in the exponential growth phase adsorbed large amounts of Ca within the EPS and mediated nucleation of ACC, while cells at the stationary/death phase neither adsorbed large amounts of Ca2+ nor mediated the formation of aragonite-like CaCO3. It is suggested that precipitation of an X-ray amorphous CaCO3 layer by cyanobacteria could serve as a protection mechanism against uncontrolled precipitation of a thermodynamically stable phase calcite on their surface. (c) 2009 Elsevier Ltd. All rights reserved.