The role of intermediate sulfur species (ISS) for isotopic fractionation processes during abiotic and chemolithoautotrophic sulfide oxidation in a natural environment

硫同位素分馏（34 S/32 S）自20世纪40年代后期以来一直用于研究化学和生物硫循环。虽然细菌硫酸盐还原过程中的大同位素分馏成功地用于解释，例如，由于硫酸盐在古海洋中的积累或早期生命的演化，对硫化物氧化过程中的分馏作用知之甚少。两个端元硫化物和硫酸盐之间的分馏通常要小得多，并且无论底物或产物是否富集都存在不一致性。这些不一致的解释是缺乏知识的氧化途径和速率，以及中间硫物种，如元素硫，多硫化物，硫代硫酸盐，亚硫酸盐，或类金属硫化物络合物（如硫代砷酸盐），潜在的34 S sounks.In拟议中的项目，我们将开发一种方法，用于硫物种选择性同位素分析的基础上分离制备色谱。在C18柱上用三氟甲磺酸甲酯衍生化后，Sn 2-和S 0将被实现分离，在AS 16柱上在碱性洗脱液中分离其它硫物种。收集的馏分中的硫将直接用活化的铜片（Sn 2-，SO）提取，或沉淀为ZnS（S2-）或BaSO 4，并通过常规方法分析为SO 2。这种物种选择性的方法的结果将进行比较，从以前的技术的端员池测定和顺序precipitations.The方法将被应用到硫化物氧化配置文件在中性到碱性温泉在黄石国家公园，美国，在那里我们检测到中间硫物种的重要物种。仅在硫化物和硫酸盐中确定34 S/32 S，我们以前的研究显示了两个温泉排水系统的不同分馏模式，从地球化学的角度来看，硫化物氧化剖面似乎相似。不同同位素趋势的原因尚不清楚。在本项目中，我们将区分物种选择性的非生物与生物分馏使用现场培养实验的化能无机硫氧化细菌Thermocrinis ruber作为模式生物。对于选定的样品，我们将测试33 S和36 S是否进一步阐明物种选择性硫化物氧化模式。我们预计，较低的源硫化物浓度增加元素硫分馏，从而增加氧化还原循环和同位素分馏。我们还预计，浓度越大的中间硫物种，包括硫代砷酸盐，更大的同位素分馏。在物种选择性池分馏后，我们将能够澄清先前报道的34 S富集在底物或产物中的不一致性，阐明硫化物氧化途径和速率，并揭示硫代谢的细节。我们的新方法和基于现场的数据将成为未来对硫化物氧化进行更一致研究的基础。

Sulfur isotope fractionation (34S/32S) has been used since the late 1940s to study the chemical and biological sulfur cycle. While large isotope fractionations during bacterial sulfate reduction were used successfully to interpret, e.g., accumulation of sulfate in ancient oceans or the evolution of early life, much less is known about fractionation during sulfide oxidation. The fractionation between the two end-members sulfide and sulfate is commonly much smaller and inconsistencies exist whether substrate or product are enriched. These inconsistencies are explained by a lack of knowledge on oxidation pathways and rates as well as intermediate sulfur species, such as elemental sulfur, polysulfides, thiosulfate, sulfite, or metalloid-sulfide complexes (e.g. thioarsenates), potentially acting as 34S sinks.In the proposed project, we will develop a method for sulfur species-selective isotope analysis based on separation by preparative chromatography. Separation of Sn2- and S0 will be achieved after derivatization with methyl triflate on a C18 column, separation of the other sulfur species in an alkaline eluent on an AS16 column. Sulfur in the collected fractions will be extracted directly with activated copper chips (Sn2-, S0), or precipitated as ZnS (S2-) or BaSO4 and analyzed by routine methods as SO2. Results of this species-selective approach will be compared to those from previous techniques of end-member pool determinations and sequential precipitations.The method will be applied to sulfide oxidation profiles at neutral to alkaline hot springs at Yellowstone National Park, USA, where we detected intermediate sulfur species as important species. Determining 34S/32S only in sulfide and sulfate, our previous study has shown different fractionation patterns for two hot spring drainages with sulfide oxidation profiles that seemed similar from a geochemical perspective. The reasons for the different isotopic trends are unclear. In the present project, we will differentiate species-selective abiotic versus biotic fractionation using on-site incubation experiments with the chemolithotrophic sulfur-oxidizing bacteria Thermocrinis ruber as model organism. For selected samples, we will test whether 33S and 36S further elucidate species-selective sulfide oxidation patterns. We expect that lower source sulfide concentrations increase elemental sulfur disproportionation, thus increase redox cycling and isotope fractionation. We also expect that the larger the concentration of intermediate sulfur species, including thioarsenates, the larger the isotope fractionation. Following fractionation in species-selective pools, we will be able to clarify previously reported inconsistencies of 34S enrichment in substrate or product, elucidate sulfide oxidation pathways and rates, and reveal details about sulfur metabolism. Our new methodology and field-based data will be a basis for more consistent studies on sulfide oxidation in the future.