Identification of polysulfides and their importance as intermediate sulfur species for electron transfers processes in anoxic aquifers

该项目的中心假设是，多硫化物作为中间硫物种，对缺氧含水层中的电子转移过程非常重要。在项目的第一部分，我们将通过反相色谱与电感耦合等离子体质谱联用，建立三氟甲磺酸甲酯衍生化后的元素硫和多硫化物的分离。通过与合成标准物质进行比较，可以在衍生化多硫化物的分析过程中对分析制品进行鉴定、定量和检测。将使用电喷雾质谱来确认合成的二甲基多硫醚的真实性。硫化物、硫代硫酸盐、多硫酸盐、亚硫酸盐和硫酸盐的形态将在已建立的阴离子交换层析方法的基础上实现。在该项目的第二部分中，将研究多硫化物作为电子穿梭对德氏硫杆菌间接还原生物和非生物合成的氢氧化铁(氢氧化铁)的重要性。我们预计，pH的轻微变化会影响中间硫物种的形态，从而显著影响电子转移机制。将测试不同浓度的初始溶解硫物种(以多硫化物、元素硫或硫代硫酸盐的形式交替添加)，以确定启动S循环介导的Fe(III)还原所需的最低硫浓度。我们将研究总硫浓度是否影响电子穿梭机制中的中间硫形态。预计将在较高的总硫浓度下形成主要产品的铁硫化物将通过X射线衍射仪和Moessbauer光谱进行鉴定和定量。直接与微生物接触的氧化铁的还原将与微生物从矿物相中分离的装置的还原进行比较。在该项目的第三部分，研究组其他成员设立的实验将用来确定多硫化物作为电子受体和供体的作用，在有溶解有机化合物的情况下用水铁水还原硫化物时，在硫歧化过程中，最后在有溶解有机物存在的缺氧含水层中，以确定在自然条件下各个过程的相关性。

The central hypothesis of the project is that polysulfides as intermediate sulfur species are important for electron transfer processes in anoxic aquifers. In the first part of the project, we will establish elemental sulfur and polysulfide separation after derivatization with methyl trifluoromethanesulfonate by reverse-phase chromatography coupled to inductively-coupled plasma mass-spectrometry. Identification, quantification, and detection of analytical artefacts during analysis of derivatized polysulfides will be possible by comparison with synthesized reference materials. Electro-spray mass-spectrometry will be used to confirm the identity of the synthesized dimethyl polysulfides. Speciation of sulfide, thiosulfate, polythionates, sulfite, and sulfate will be achieved based on established anion-exchange-chromatographic methods. In the second part of the project, the importance of polysulfides as electron shuttles for the indirect reduction of both biogenic and abiogenically synthesized ferric iron hydroxide (ferrihydrite) by Sulfurospirillum deleyianum will be investigated. We expect that slight changes in pH influence speciation of intermediate sulfur species and thus the electron transfer mechanisms significantly. Different concentrations of initially present dissolved sulfur species (added alternatively in form of polysulfides, elemental sulfur, or thiosulfate) will be tested to determine the minimum sulfur concentration needed to start the S-cycle-mediated Fe(III) reduction. We will investigate whether total sulfur concentration affects intermediate sulfur speciation within the electron shuttle mechanism. Iron sulfides expected to form as major products at higher total sulfur concentrations will be identified and quantified by X-ray diffractometry and Moessbauer spectroscopy. Reduction of iron (hydr)oxides in direct contact with microorganisms will be compared to reduction in setups where microorganisms are separated from the mineral phase. In the third part of the project, experiments setup by other members of the research group will be used to determine the role of polysulfides as electron acceptors and donors during sulfide oxidation by ferrihydrite reduction in the presence of dissolved organic compounds, during sulfur disproportionation, and finally in an anoxic aquifer in the presence of dissolved organic matter to determine the relevance of the individual processes under natural conditions.