The Kinetics of Microbial Sulfuric Acid Speleogenesis

地球地下有无数的栖息地，微生物可以操纵化学形式的能量，改变地质环境来获取营养。这些营养化学物质的群落利用无机底物的氧化还原转化产生的能量，而不需要碳还原或外来常量营养素的流入。在过去的四年里，我们一直在描述下凯恩洞穴(LKC)的地球化学和微生物学，这是一个硫酸盐碳酸盐洞穴生态系统，是深部地下环境的可接近的类似物。在这里，化石型硫(S)氧化形成了一个复杂的微生物生态系统的基础，这些微生物似乎可以加速硫化物的氧化成硫酸盐，产生质子，并可能通过溶解石灰石来改变它们的栖息地。我们的初步结果表明，基于S的陆地微生物群落具有更广泛的意义，这提出了关于地下生态系统、S新陈代谢、S和C循环的耦合以及地质后果的新问题。科学价值：我们之前的工作已经确定，地下化学自养微生物种群在LKC的硫化物水域中蓬勃发展，氧化硫化物。质量平衡计算表明，标准的硫酸生成(SAS)模型--硫化氢的挥发和洞壁上的自氧化作用--是微不足道的，几乎所有的硫化物在水生体系中都被氧化了。然而，微生物是否会加速硫化物氧化和洞穴形成，直接参与洞穴形成的地质过程，这一问题仍然没有答案。我们建议利用LKC的自然实验室，结合对照的实验室微宇宙实验，来研究微生物SAS作为岩溶作用机制的重要性。这项建议将解决以下问题：1-水生微生物群落如何加速石灰岩的风化？2-具有不同S氧化机制的不同SOB种群是否在不同程度上影响石灰岩的风化？群落组成重要吗？3-矿物学对微生物栖息地的重要性是什么？将使用间歇反应器和流通式恒化器考察选定的单一培养和环境混合种群群落对方解石和白云石溶解速率的影响。我们将使用我们在LKC以前的工作中开发的工具和技术来表征洞穴的地球化学，以及使用独立于培养的方法来描述野外系统和实验室反应堆中的微生物群落。然后，将利用SSU rDNA系统发育学、RFLP、FISH和PLFA分析，将速率测量与详细的分子微生物学特征相结合，以表征群落对岩溶作用的影响。将研究微生物在碳酸盐风化中的作用，以及矿物化学在定义这些嗜中性微生物种群栖息地方面的作用。广泛影响：硫酸喷发作用可能是一种广泛的现象，可能导致加速岩溶作用和区域关键水源含水层网络的发展，包括德克萨斯州中部的爱德华兹含水层及其特有的茎类和嗜硫藻。该项目对我们理解含水层和石油储集层的岩溶孔隙度的发育，以及我们对地下微生物生态学的认识都有重要的意义。特别是，该项目将加强我们对矿物学在微生物生态学中的作用的了解，并使我们能够更好地了解地下微生物生存和生长的机制，以及对岩溶含水层中病原体运输的影响。该项目将直接支持德克萨斯大学的一名博士、一名硕士和一名本科生，并将他们介绍给正在发展中的微生物地球化学和地球微生物学领域。LKC网站已经成为直接检验SAS岩溶理论的典型地点，我们之前的研究结果已经在PBS-NOVA上公布，并由BBC在整个欧洲转播。我们的工作结果也成为德克萨斯大学两个研究生班的中心主题，这些特征良好的存档样本被用来向地球微生物学项目的新研究生教授分子技术

EAR-0617160BENNETTThe Earth's subsurface contains innumerable habitats occupied by microorganisms that manipulate chemical forms of energy and alter the geologic surroundings to scavenge nutrients. These chemolithotrophic communities utilize energy from redox transformation of inorganic substrates, without an influx of reduced carbon or allochthonous macronutrients. For the last four years we have been characterizing the geochemistry and microbiology of Lower Kane Cave (LKC), a sulfidic carbonate cave ecosystem, as an accessible analog for deep subsurface environments. Here chemolithotrophic sulfur (S) oxidation forms the base of a complex microbial ecosystem, and these microbes appear to accelerate the oxidation of sulfide to sulfate, generating proton and potentially modifying their habitat by dissolving limestone. Our preliminary results suggest a much broader significance of terrestrial S-based microbial communities, raising new questions about subsurface ecosystems, S metabolism, the coupling of S and C cycles, and the geological consequences.Scientific Merit: Our previous work has established that a subsurface chemoautotrophic microbial population thrives in the sulfidic waters of LKC, oxidizing sulfide. Mass balance calculations show that the standard model of sulfuric acid speleogenesis (SAS), the volatilization of H2S and autoxidation on the cave wall, is insignificant, and almost all sulfide is oxidized in the aquatic system. Unanswered, however, is the question of whether the microbes accelerate sulfide oxidation and speleogenesis, directly participating in the geologic process of speleogenesis. We propose to use the natural laboratory of LKC, combined with controlled laboratory microcosm experiments, to examine the importance of microbial SAS as a mechanism of karstification. This proposal will address the following questions:1- How does the aquatic microbial community accelerate limestone weathering?2- Do the different SOB populations, with diverse S-oxidation mechanisms, influence limestone weathering to different degrees? Is community composition important?3- What is the importance of mineralogy to microbial habitat?Batch reactors and flow-through chemostat reactors will be used to examine selected monoculture and environmental mixed population community influence on calcite and dolomite dissolution rate. We will use the tools and techniques developed from our previous work at LKC to characterize the cave geochemistry, and the microbial communities in both the field system and the laboratory reactors using culture-independent methods. The rate measurements will then be combined with the detailed molecular microbiological characterization using SSU Rdna phylogenetics, RFLP, FISH and PLFA analysis to characterize the influence of community on karstification. Both the role of microbes in carbonate weathering, and the role of mineral chemistry in defining the habitat for these neutrophilic microbial populations will be examined.Broader Impacts: Sulfuric acid speleogenesis is potentially a widespread phenomenon that could be responsible for accelerated karstification and development of aquifer networks for regionally critical source of water, including the Edwards Aquifer of central Texas and its endemic stygobites and stygophiles. This project has implications for our understanding of the development of karst porosity for both aquifer and petroleum reservoirs, and our knowledge of subsurface microbial ecology. In particular this project will enhance our understanding of the role of mineralogy in microbial ecology, and allow a better understanding of the mechanisms for microbial survival and growth in the subsurface, with implications for pathogen transport in karst aquifers. This project will directly support one PhD, one MS, and one undergraduate student at the University of Texas, and introduce them to the developing field of microbial geochemistry and geomicrobiology. The LKC site has become a type locality for directly examining the theory of SAS in karstification, and the results from our previous research have been presented on PBS-NOVA, and rebroadcast by the BBC throughout Europe. The results from our work have also become a central theme in two graduate classes at UT, and the well characterized archived samples are used to teach molecular techniques to new graduate students in the geomicrobiology program