Does organic sulfur make a significant and overlooked contribution to sediment sulfate reduction in low-sulfate environments?

有机硫是否对低硫酸盐环境中沉积物硫酸盐的减少做出了重大但被忽视的贡献？

• 批准号: 1754061
• 负责人: Sergei Katsev
• 金额: $ 52.2万
• 依托单位: University of Minnesota Duluth
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-08-01 至 2023-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1754061&HistoricalAwards=false
• 关键词: Does; organic; sulfur; make; significant

Sulfur is an ever-present component of living matter. As aquatic organisms grow, die, and decay, sulfur is exchanged between the organisms and their environment, cycling between its organic forms in living cells and inorganic forms in ambient water. An important process in the geochemistry of sulfur is sulfate reduction. This process, carried out in the environment by microorganisms in the absence of oxygen, converts sulfate, the oxidized and commonly available form of inorganic sulfur, into hydrogen sulfide, which is highly reactive and generally toxic to other organisms. This process has multiple environmental significances: it regulates the fluxes of important nutrients such as phosphorus and pollutants such as mercury; it is a pathway by which significant amounts of organic carbon are converted into carbon dioxide and low molecular weight carboxylic acids; and it affects the life cycles of commercially important aquatic plants such as wild rice. Over geological time scales, it is responsible for the formation of iron sulfides, which are preserved in sedimentary rocks and contain the record of environmental conditions dating back to the earliest stages of Earth's history. Present understanding of sulfate reduction, however, has been largely shaped by studies in marine settings where sulfate is abundant and easily available to organisms from seawater. The situation is different in freshwater lakes, rivers, and other low-sulfate environments, which include the oceans of distant geologic past and sediments deep below seafloor. Organic sulfur appears to be a much more important source of sulfur for sulfate reduction in these low-sulfate environments, however the pathways by which it circulates and the magnitude of its effects in different conditions are unknown. A team of geochemists, organic chemists, and geomicrobiologists from the University of Minnesota Duluth will address these questions by studying the sulfur transformations and relevant microorganisms, focusing on Lake Superior and its largest American tributary as the study area. They will collect sediments, analyze them for geochemically relevant sulfur species, measure reaction rates between these different species, and perform genetic analyses to identify key involved microbes. If the initial hypotheses are confirmed, the results are likely to transform the current paradigm of sulfur chemistry in such low-sulfate environments, influencing several scientific disciplines and providing a foundation for better environmental management practices. The project will support two beginning investigators and will train two graduate and several undergraduate students. Research cruises will provide no-cost support for several collaborative efforts on Lake Superior. Results, models, and methods will be incorporated into an innovative Limnology curriculum being developed by the PIs with NSF support. Findings will be communicated to public through a series of talks, K-12 teacher education events including a teacher education cruise on Lake Superior aboard the R/V Blue Heron broadcasted on YouTube, and exhibitions at Duluth Freshwater Aquarium. Microbially mediated sulfate reduction in aquatic sediments mineralizes organic carbon, generates hydrogen sulfide, and mediates the geochemical cycles of other elements, such as iron, phosphorus, and mercury. While organic matter contains a number of sulfur compounds, little is known of the fate of this organic sulfur pool during mineralization and more importantly its contribution to the inorganic sulfur cycle that fuels sulfate reduction. The current paradigm of sulfate reduction involves diffusion of sulfur from overlying water into the sediments where sulfur-reducing microorganisms are present. Contrary to the paradigm, modeling and preliminary results demonstrate that under low-sulfate conditions organic sulfur buried in sediment may be the dominant source of sulfur for sulfate reduction, and once mobilized, via microbial biotransformation, may be exported to the overlying water column. Contributions from organic sulfur may be pervasive in environments such as oligotrophic freshwater lakes or the oceans of the geologic past. By characterizing the organic sulfur transformations in sediments across a range of sulfate and organic carbon levels in Lake Superior and its largest American tributary, investigators will address the following questions under a range of environmental conditions: A. To what extent does organic sulfur contribute to the pool of sulfur that fuels sulfate reduction? B. Does organic sulfur undergo cryptic, microbially-mediated biogeochemical transformations, and what microorganisms are responsible for these transformations? They have assembled a multidisciplinary research team that combines expertise in sediment geochemistry, organic geochemistry, and geomicrobiology to address these objectives using sediment characterizations, rate measurements, molecular characterizations of microbial communities, and modeling. The results will quantify an important part of the diagenetic sulfur cycle that has received little attention despite its potential significance in environments such as freshwater lakes, deep subsurface, and the low sulfate oceans of the geological past. Verifying the proposed hypotheses may lead to reevaluation of the geochemical cycles of sulfur and associated elements such as iron and nitrogen, including cryptic reactions in the sulfate-methane transition zone; reinterpretation of the origins of the isotopic signatures of sulfur preserved in both modern aquatic sediments and ancient sedimentary rocks; and conservation and management practices in sulfide affected water bodies. The project will generate novel microbial and geochemical data that will be publicly available.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

硫是生命物质中一直存在的一种成分。随着水生生物的生长、死亡和腐烂，硫在生物和它们的环境之间进行交换，在活细胞中的有机形式和环境水中的无机形式之间循环。硫酸盐还原是硫的地球化学过程中的一个重要过程。这一过程由微生物在没有氧气的环境中进行，将硫酸盐--无机硫的氧化和常见形式--转化为硫化氢，后者具有很高的活性，通常对其他生物有害。这一过程具有多重环境意义：它调节磷等重要营养物质和汞等污染物的通量；它是大量有机碳转化为二氧化碳和低分子羧酸的途径；它影响野生水稻等具有重要商业价值的水生植物的生活史。在地质时间尺度上，它负责形成硫化物，这些硫化物保存在沉积岩中，包含了可追溯到地球历史最早阶段的环境条件的记录。然而，目前对硫酸盐还原的理解在很大程度上是由海洋环境中的研究形成的，在海洋环境中，硫酸盐丰富，生物很容易从海水中获得硫酸盐。淡水湖泊、河流和其他低硫酸盐环境中的情况则不同，这些环境包括遥远的地质过去的海洋和海底深处的沉积物。在这些低硫酸盐环境中，有机硫似乎是硫酸盐还原的一个更重要的硫来源，但它在不同条件下的循环途径和影响的大小尚不清楚。来自明尼苏达德卢斯大学的一个由地球化学家、有机化学家和地质微生物学家组成的团队将通过研究硫的转化和相关微生物来解决这些问题，重点是以苏必利尔湖及其美国最大的支流为研究区域。他们将收集沉积物，分析它们的地球化学相关硫物种，测量这些不同物种之间的反应速度，并进行遗传分析，以确定关键的相关微生物。如果最初的假设得到证实，结果可能会改变目前在这种低硫酸盐环境中的硫磺化学范式，影响几个科学学科，并为更好的环境管理实践提供基础。该项目将支持两名初级研究人员，并将培养两名研究生和几名本科生。研究巡航将为苏必利尔湖上的几项合作努力提供免费支持。结果、模型和方法将被纳入到由PIS在NSF支持下开发的创新湖沼学课程中。调查结果将通过一系列讲座、K-12教师教育活动，包括在YouTube上播放的R/V蓝鹭号在苏必利尔湖上的教师培训邮轮，以及德卢斯淡水水族馆的展览向公众公布。微生物介导的水生沉积物中的硫酸盐还原作用使有机碳矿化，生成硫化氢，并调节铁、磷和汞等其他元素的地球化学循环。虽然有机质含有大量的硫化物，但人们对这个有机硫库在成矿过程中的命运知之甚少，更重要的是，它在推动硫酸盐还原的无机硫循环中的作用鲜为人知。目前硫酸盐还原的范例涉及将硫从上覆水扩散到沉积物中，那里存在硫磺还原微生物。与该范式相反，模型和初步结果表明，在低硫酸盐条件下，埋藏在沉积物中的有机硫可能是硫酸盐还原的主要硫来源，一旦被微生物生物转化动员起来，就可能被输出到上覆水体。有机硫的贡献可能普遍存在于一些环境中，例如营养贫乏的淡水湖或地质历史时期的海洋。通过表征苏必利尔湖及其美国最大支流中一系列硫酸盐和有机碳水平的沉积物中有机硫的转化，研究人员将在一系列环境条件下解决以下问题：A.有机硫在多大程度上有助于推动硫酸盐还原的硫磺池？B.有机硫是否经历了隐蔽的、微生物介导的生物地球化学转化？哪些微生物对这些转化负责？他们组建了一个多学科的研究团队，将沉积物地球化学、有机地球化学和地质微生物学的专业知识结合起来，通过沉积物表征、速率测量、微生物群落的分子表征和建模来解决这些目标。这些结果将量化成岩硫循环的一个重要部分，尽管它在地质过去的淡水湖、地下深处和低硫酸盐海洋等环境中具有潜在的意义，但很少受到关注。验证提出的假设可能导致重新评估硫及其相关元素，如铁和氮的地球化学循环，包括硫酸盐-甲烷过渡带中的神秘反应；重新解释现代水生沉积物和古代沉积岩中保存的硫的同位素特征的来源；以及受硫化物影响的水体的养护和管理做法。该项目将产生新的微生物和地球化学数据，并将公开提供。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Organic sulfur was integral to the Archean sulfur cycle

• DOI: 10.1038/s41467-019-12396-y
• 发表时间: 2019-10-07
• 期刊: NATURE COMMUNICATIONS
• 影响因子: 16.6
• 作者: Fakhraee, Mojtaba;Katsev, Sergei
• 通讯作者: Katsev, Sergei

Widespread occurrence of filamentous Thioploca bacteria in low-sulfate Great Lakes sediments with implications for sulfur and nitrogen cycling

低硫酸盐五大湖沉积物中丝状硫孢菌的广泛存在对硫和氮循环的影响

• DOI: 10.1016/j.jglr.2023.07.003
• 发表时间: 2023
• 期刊: Journal of Great Lakes Research
• 影响因子: 2.2
• 作者: McKay, Elizabeth;Katsev, Sergei;Malkin, Sairah;Ozersky, Ted
• 通讯作者: Ozersky, Ted