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、扩散流区浅层次表层和大洋中脊热液羽流中硫生物化学循环的关键中间物种。尽管火山喷发后在水柱中发现的絮状物主要是硫，而且许多从喷口分离出来的微生物利用硫，但在烟囱沉积物中没有发现显著的硫储藏，这表明元素硫在地下的周转率很高。在与水热混合环境相关的温度和pH条件下，非生物SO氧化和还原的动力学速率常数是未知的，尽管它们对于限制SO在H2(AQ)和O2(AQ)存在下的亚稳性从而限制其生物有效性是至关重要的。在与环境相关的条件下，也没有研究描述SO的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生理学之间存在差异。在这个项目中，华盛顿圣路易斯大学(WU)和华盛顿卡内基研究所(CIW)的研究人员将在T、pH和H2(AQ)-O2(AQ)浓度范围内对元素硫的非生物氧化/还原动力学进行实验评估，该范围与玄武岩和超镁铁质热液系统的浅次表层有关：250巴、40-120℃、4-9、90.1-20 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，以确定分馏是否随着环境条件开始抑制生长而增加，就像SO4还原细菌一样。通过表征来自喷口系统的SO氧化/减少高温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进全球海洋硫循环的相关羽流环境的影响。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，建立了吴和CIW之间的新合作，并通过促进该项目的领导作用，将一名女性科学家重新引入全职研究。将支持两个不同的本科生研究项目，涉及生物学、地球化学和计算机科学。此外，研究小组将为中学生开发一个在线互动模拟，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。这项教育推广活动还将与一名中学教师建立工作关系，该教师具有适应在线学习的科学数据和方法的经验。

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.