Borilova Sarka, Mandl Martin, Zeman Josef, Kucera Jiri, Pakostova Eva, Janiczek Oldrich, Tuovinen Olli H
Department of Biochemistry, Faculty of Science, Masaryk University, Brno, Czechia.
Department of Geological Sciences, Faculty of Science, Masaryk University, Brno, Czechia.
Front Microbiol. 2018 Dec 18;9:3134. doi: 10.3389/fmicb.2018.03134. eCollection 2018.
According to the literature, pyrite (FeS) oxidation has been previously determined to involve thiosulfate as the first aqueous intermediate sulfur product, which is further oxidized to sulfate. In the present study, pyrite oxidation by was studied using electrochemical and metabolic approaches in an effort to extend existing knowledge on the oxidation mechanism. Due to the small surface area, the reaction rate of a compact pyrite electrode in the form of polycrystalline pyrite aggregate in suspension was very slow at a spontaneously formed high redox potential. The slow rate made it possible to investigate the oxidation process in detail over a term of 100 days. Using electrochemical parameters from polarization curves and levels of released iron, the number of exchanged electrons per pyrite molecule was estimated. The values close to 14 and 2 electrons were determined for the oxidation with and without bacteria, respectively. These results indicated that sulfate was the dominant first aqueous sulfur species formed in the presence of bacteria and elemental sulfur was predominantly formed without bacteria. The stoichiometric calculations are consistent with high iron-oxidizing activities of bacteria that continually keep the released iron in the ferric form, resulting in a high redox potential. The sulfur entity of pyrite was oxidized to sulfate by Fe without intermediate thiosulfate under these conditions. Cell attachment on the corroded pyrite electrode surface was documented although pyrite surface corrosion by Fe was evident without bacterial participation. Attached cells may be important in initiating the oxidation of the pyrite surface to release iron from the mineral. During the active phase of oxidation of a pyrite concentrate sample, the ATP levels in attached and planktonic bacteria were consistent with previously established ATP content of iron-oxidizing cells. No significant upregulation of three essential genes involved in energy metabolism of sulfur compounds was observed in the planktonic cells, which represented the dominant biomass in the pyrite culture. The study demonstrated the formation of sulfate as the first dissolved sulfur species with iron-oxidizing bacteria under high redox potential conditions. Minor aqueous sulfur intermediates may be formed but as a result of side reactions.
根据文献记载，黄铁矿（FeS）氧化过程中先前已确定硫代硫酸盐是首个水相中间硫产物，其会进一步氧化为硫酸盐。在本研究中，采用电化学和代谢方法研究了 对黄铁矿的氧化作用，旨在扩展有关氧化机制的现有知识。由于表面积较小，多晶黄铁矿聚集体形式的致密黄铁矿电极在 悬浮液中，于自发形成的高氧化还原电位下反应速率非常缓慢。这种缓慢的速率使得能够在100天的时间内详细研究氧化过程。利用极化曲线的电化学参数和释放铁的水平，估算了每个黄铁矿分子交换的电子数。对于有菌和无菌氧化，分别确定的值接近14和2个电子。这些结果表明，在有细菌存在的情况下，硫酸盐是形成的主要首个水相硫物种，而在无菌情况下主要形成元素硫。化学计量计算与细菌的高铁氧化活性一致，细菌持续将释放的铁保持在三价铁形式，从而产生高氧化还原电位。在这些条件下，黄铁矿的硫实体被Fe氧化为硫酸盐，没有中间硫代硫酸盐。尽管在没有细菌参与的情况下Fe对黄铁矿表面的腐蚀很明显，但记录到了细胞附着在被腐蚀的黄铁矿电极表面。附着的细胞可能在引发黄铁矿表面氧化以从矿物中释放铁方面很重要。在黄铁矿精矿样品氧化的活跃阶段，附着细菌和浮游细菌中的ATP水平与先前确定的铁氧化细胞的ATP含量一致。在浮游细胞中未观察到参与硫化合物能量代谢的三个必需基因有明显上调，浮游细胞是黄铁矿培养物中的主要生物量。该研究证明了在高氧化还原电位条件下，铁氧化细菌存在时硫酸盐作为首个溶解硫物种的形成。可能会形成少量水相硫中间体，但这是副反应的结果。
