Miot J, Benzerara K, Morin G, Bernard S, Beyssac O, Larquet E, Kappler A, Guyot F
Institut de Minéralogie et de Physique des Milieux Condensés, Universités Paris 6 et Paris 7, Paris, France.
Geobiology. 2009 Jun;7(3):373-84. doi: 10.1111/j.1472-4669.2009.00203.x.
In phosphate-rich environments, vivianite (Fe(II)(3)(PO(4))(2), 8H(2)O) is an important sink for dissolved Fe(II) and is considered as a very stable mineral due to its low solubility at neutral pH. In the present study, we report the mineralogical transformation of vivianite in cultures of the nitrate-reducing iron-oxidizing bacterial strain BoFeN1 in the presence of dissolved Fe(II). Vivianite was first transformed into a greenish phase consisting mostly of an amorphous mixed valence Fe-phosphate. This precipitate became progressively orange and the final product of iron oxidation consisted of an amorphous Fe(III)-phosphate. The sub-micrometer analysis by scanning transmission X-ray microscopy of the iron redox state in samples collected at different stages of the culture indicated that iron was progressively oxidized at the contact of the bacteria and at a distance from the cells in extracellular minerals. Iron oxidation in the extracellular minerals was delayed by a few days compared with cell-associated Fe-minerals. This led to strong differences of Fe redox in between these two types of minerals and finally to local heterogeneities of redox within the sample. In the absence of dissolved Fe(II), vivianite was not significantly transformed by BoFeN1. Whereas Fe(II) oxidation at the cell contact is most probably directly catalyzed by the bacteria, vivianite transformation at a distance from the cells might result from oxidation by nitrite. In addition, processes leading to the export of Fe(III) from bacterial oxidation sites to extracellular minerals are discussed including some involving colloids observed by cryo-transmission electron microscopy in the culture medium.
在富含磷酸盐的环境中，蓝铁矿（Fe(II)₃(PO₄)₂·8H₂O）是溶解态Fe(II)的重要汇，并且由于其在中性pH下的低溶解度而被认为是一种非常稳定的矿物。在本研究中，我们报道了在溶解态Fe(II)存在的情况下，硝酸盐还原型铁氧化细菌菌株BoFeN1培养物中蓝铁矿的矿物学转变。蓝铁矿首先转变为一种主要由无定形混合价态铁磷酸盐组成的绿色相。这种沉淀物逐渐变为橙色，铁氧化的最终产物是一种无定形的Fe(III)磷酸盐。通过扫描透射X射线显微镜对培养不同阶段收集的样品中铁的氧化还原状态进行亚微米分析表明，铁在细菌接触处以及细胞外矿物中离细胞一定距离处逐渐被氧化。与细胞相关的铁矿物相比，细胞外矿物中的铁氧化延迟了几天。这导致了这两种类型矿物之间铁氧化还原的强烈差异，最终导致样品内氧化还原的局部不均匀性。在没有溶解态Fe(II)的情况下，BoFeN1对蓝铁矿没有显著转化作用。虽然细胞接触处的Fe(II)氧化很可能直接由细菌催化，但离细胞一定距离处的蓝铁矿转化可能是由亚硝酸盐氧化导致的。此外，还讨论了导致Fe(III)从细菌氧化位点输出到细胞外矿物的过程，包括一些涉及在培养基中通过低温透射电子显微镜观察到的胶体的过程。
