Mineralogical and morphological constraints on the reduction of Fe(III) minerals by Geobacter sulfurreducens
Mineralogical and morphological constraints on the reduction of Fe(III) minerals by Geobacter sulfurreducens
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DOI：
10.1016/j.gca.2009.04.009
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发表时间：
2009-07-15
影响因子：
5
通讯作者：
Vaughan, D. J.
中科院分区：
文献类型：
--
作者：
Cutting, R. S.;Coker, V. S.;Vaughan, D. J.
采用微生物学技术，结合X射线衍射（XRD）、透射电子显微镜（TEM）和X射线光电子能谱（XPS）研究了含Fe（III）矿物赤铁矿、针铁矿、纤铁矿、铁氧铁矿、福特水铁矿、赤霞铁矿和施氏锰矿的合成样品被Geodensulfreducens生物介导的还原过程。这种方法的组合提供了独特的见解，在一个给定的矿物结晶度的微妙变化对地球化学过程的影响，并强调了（oxyhydr）氧化物微晶形态在确定发生在一个给定的矿物相的变化的重要性。还强调了相对于起始材料的比表面积的生物Fe（III）还原率归一化所产生的问题。这些问题主要是由颗粒聚集引起的，并且在使用分光光度测定来监测减少时会变得更加复杂。例如，对于具有不同堆叠（如XRD和TEM研究所示）但几乎相同表面积的两种合成铁氧植物观察到的Fe（III）还原的初始速率显著不同。微生物学和高分辨率TEM研究表明，赤铁矿和针铁矿对有限量的Fe（III）还原敏感，如在与G.硫还原物和孕育过程中结晶针铁矿板条状物上结节状结构的生长。Lepidocrocite和akaganeite很容易转化为磁铁矿和针铁矿的混合物，XRD数据表明，磁铁矿的比例增加的转化产物中的结晶度的起始材料的降低。蒽醌-2，6-二磺酸盐（AQDS）作为电子穿梭的存在下，增加了初始速率和长期的生物Fe（III）的还原程度为所有的合成矿物检查。高分辨率XPS表明细微的，但可测量的差异，在矿物表面的Fe（III）：Fe（II）的比例延长孵育。例如，对于结晶较差的施威特曼石，Fe 2 p（3/2）峰的解卷积表明，近表面区域的Fe（III）：Fe（II）比从起始材料中的1.0变化到与G孵育144小时后的0.9。在10 μ M AQDS存在下，在相同的孵育期后，这些结果对铁的地球化学循环具有重要意义。(c)2009爱思唯尔有限公司保留所有权利。
The biologically-mediated reduction of synthetic samples of the Fe(III)-bearing minerals hematite, goethite, lepidocrocite, feroxhyte, ford ferrihydrite, akaganeite and schwertmannite by Geobacter sulfurreducens has been investigated using microbiological techniques in conjunction with X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). This combination of approaches offers unique insights into the influence of subtle variations in the crystallinity of a given mineral on biogeochemical processes, and has highlighted the importance of (oxyhydr)oxide crystallite morphology in determining the changes occurring in a given mineral phase. Problems arising from normalising the biological Fe(III) reduction rates relative to the specific surface areas of the starting materials are also highlighted. These problems are caused primarily by particle aggregation, and compounded when using spectrophotometric assays to monitor reduction. For example, the initial rates of Fe(III) reduction observed for two synthetic feroxyhytes with different crystallinities (as shown by XRD and TEM studies) but almost identical surface areas, differ substantially. Both microbiological and high-resolution TEM studies show that hematite and goethite are susceptible to limited amounts of Fe(III) reduction, as evidenced by the accumulation of Fe(II) during incubation with G. sulfurreducens and the growth of nodular structures on crystalline goethite laths during incubation. Lepidocrocite and akaganeite readily transform into mixtures of magnetite and goethite, and XRD data indicate that the proportion of magnetite increases within the transformation products as the crystallinity of the starting material decreases. The presence of anthraquinone-2,6-disulfonate (AQDS) as an electron shuttle increases both the initial rate and longer term extent of biological Fe(III) reduction for all of the synthetic minerals examined. High-resolution XPS indicates subtle but measurable differences in the Fe(III):Fe(II) ratios at the mineral surfaces following extended incubation. For example, for a poorly crystalline schwertmannite, deconvolution of the Fe2p(3/2) peak suggests that the Fe(III):Fe(II) ratio of the near-surface regions varies from 1.0 in the starting material to 0.9 following 144 h of incubation with G. sulfurreducens, and to 0.75 following the same incubation period in the presence of 10 mu M AQDS. These results have important implications for the biogeochemical cycling of iron. (c) 2009 Elsevier Ltd. All rights reserved.