Collaborative Research: Kinetics and Stable Isotopic Fractionation for Abiotic and Microbial Transformations of Elemental Sulfur at Seafloor Hydrothermal Environments

元素硫 (So) 是烟囱沉积物、扩散流区域浅层地下以及大洋中脊热液羽流中生物化学硫循环的关键中间物种。尽管火山喷发后水柱中发现的絮凝物主要是 So，并且发现许多来自喷口的微生物分离物都利用 So，但在烟囱沉积物中没有发现明显的 So 储层，这表明地下元素硫的周转率很高。非生物 So 氧化和还原的动力学速率常数未知，尽管它们对于在 H2(aq) 和 O2(aq) 存在下、在与水热混合环境相关的温度和 pH 条件下限制 So 的亚稳定性和生物利用度至关重要。也没有在环境相关条件下研究描述 So 微生物转化的速率常数。因此，基于能量学的预测与在实验室条件下分离和生长的微生物的观察到的生理学之间存在差异。准确和现实的生物和非生物动力学速率常数对于模拟生物地球化学转化至关重要，涉及在地下玄武岩和超镁铁质热液系统中发现的可变 pH 和氧化还原条件下的中间硫物种和活性微生物群落。在该项目中，圣路易斯华盛顿大学 (WU) 和华盛顿卡内基研究所 (CIW) 的研究人员将通过实验评估元素硫非生物氧化/还原的动力学。与玄武岩和超镁铁质热液系统浅层地下相关的 T、pH 和 H2(aq)-O2(aq) 浓度：250 巴、40-120 摄氏度、pH 4 - 9、0.1-20 mM H2(aq) 和 0-0.25 mM O2(aq)。同时，他们将表征介导元素硫氧化还原转化的三种关键细菌的分解代谢反应速率，以确定随着环境条件开始抑制生长，分馏是否会增加，就像 SO4 还原细菌所看到的那样。通过表征来自喷口系统的SO-氧化/还原嗜热自养生物的地球化学和同位素效应，他们希望能够评估复杂的地下微生物生态系统对促成全球海洋硫循环的相关羽流环境的影响。更广泛的影响：拟议的项目汇集了实验、微生物和硫同位素专业知识，在WU和CIW之间建立了新的合作，并通过促进在这一领域的领导作用，重新将一位女科学家重新引入全职研究。项目。将支持两个跨生物学、地球化学和计算机科学的独特本科研究项目。此外，研究团队将为中学生开发在线交互式模拟，使他们能够在学生主导的调查中使用这项研究产生的真实科学数据。这项教育外展活动还将与一名在采用科学数据和方法进行在线学习方面拥有丰富经验的中学教师建立工作关系。

Elemental sulfur (So) is a key intermediate species for biochemical sulfur cycling in chimney deposits, the shallow subsurface in diffuse flow areas, and hydrothermal plumes at mid-ocean ridges. Although the floc found in the water column after a volcanic eruption is predominantly So and many microbial isolates from vents are found to utilize So, no significant reservoir of So has been found in chimney deposits, suggesting high turnover rates of elemental sulfur in the subsurface. The kinetic rate constants for abiotic So oxidation and reduction are unknown, even though they are critical for constraining the metastability, and thus bioavailability, of So in the presence of H2(aq) and O2(aq) at temperatures and pH conditions relevant to hydrothermal mixing environments. Nor have the rate constants describing microbial transformations of So been studied at environmentally relevant conditions. As a result, there is a discrepancy between predictions based on energetics and the observed physiology of microorganisms that have been isolated and grown in laboratory conditions. Accurate and realistic biotic and abiotic kinetic rate constants are essential for modeling biogeochemical transformations involving intermediate sulfur species and active microbial consortia at the variable pH and redox conditions found in subsurface underlying basalt- and ultramafic-hosted hydrothermal systems.In this project, researchers at Washington University of St. Louis (WU) and at the Carnegie Institute of Washington (CIW) will experimentally evaluate the kinetics of elemental sulfur abiotic oxidation/reduction at a range of T, pH and H2(aq)-O2(aq) concentrations relevant to the shallow subsurface of basalt and ultramafic hydrothermal systems: 250 bars, 40-120 deg C, pH 4 - 9, 0.1-20 mM H2(aq) and 0-0.25 mM O2(aq). Simultaneously, they will characterize the catabolic reaction rates of thre key bacterial species that mediate elemental sulfur redox transformations to determine if fractionation increases as environmental conditions begin to inhibit growth, as has been seen for SO4 reducing bacteria. By characterizing the geochemical and isotopic effect of So-oxidizing/reducing thermophilic autotrophs from vent systems, they expect to be able to evaluate the impact of complex subsurface microbial ecological systems on associated plume environments contributing to the global ocean sulfur cycle.Broader impacts: The proposed project brings together experimental, microbial, and sulfur isotope expertise, establishes a new collaboration between WU and the CIW, and reintroduces a female scientist back into full-time research by facilitating a leading role in this project. Two distinct undergraduate research projects crossing biology, geochemistry, and computer science will be supported. Furthermore, the research team will develop an online interactive simulation for secondary students that will allow them to use the real scientific data produced by this study in student-driven investigations. This educational outreach activity will also establish a working relationship with a secondary school teacher with experience adapting scientific data and methods for online learning.