Microbial Community Controls on Sulfide Oxidation Rates and Cave Formation in a Subsurface Biogeochemical System

该项目旨在发现控制微生物群落聚集和多样性的规则，以及这些对地球化学过程速率的影响。这些问题在大多数生态系统中很难解决，因为那里的微生物多样性非常高，空间异质性很大。Frasassi洞穴生态系统远离地表固定碳和氮的来源，仅以硫氧化为燃料，因此微生物活动可能与硫酸生产直接相关。该洞穴中存在中性和pH值为0-1的硫氧化菌群，并将这些菌群类型进行比较，以验证微生物多样性和菌群功能的假设。例如，我们假设微生物多样性受到可用电子供体和电子受体数量的强烈控制，而不是受到极端环境（如低pH）的限制。在这种情况下，pH 0-1和中性Frasassi微生物群落的多样性将低于先前研究的pH 0-1酸性矿山排水系统，其中铁和硫电子供体都是可用的。该项目还旨在确定对硫酸生产（溶洞溶解）的生物和地质控制。分子生物学方法将用于量化微生物种群，地球化学方法将用于记录和监测洞穴生境和微生物培养，脂质和同位素标记方法将用于量化生物量和鉴定洞穴群落中的自养微生物。该项目将涉及6名本科论文学生，并开发一个教育模块，该模块将被纳入意大利卡尔顿学院非常成功的地质学项目。这项工作将培养年轻的科学家，使他们接受地质微生物学的跨学科培训，并发表论文，确定控制地下微生物群落的结构和功能的因素，这些因素负责硫酸的产生和洞穴的形成。更一般地说，了解微生物群落是如何聚集的，以及这些聚集模式如何影响可用资源的利用，是理解古代和现代环境的生物地球化学的关键组成部分。

This project aims to discover rules governing microbial community assembly and diversity, and the effects of these on geochemical process rates. These questions are difficult to address in most ecosystems, where microbial diversity is very high and spatial heterogeneities are large. The Frasassi cave ecosystem is distant from surface sources of fixed carbon and nitrogen and is fueled only by sulfur oxidation, so that microbial activity can be directly related to sulfuric acid production. The cave hosts both neutral and pH 0-1 sulfur-oxidizing communities, and these community types will be compared to test hypothesis about microbial diversity and community function. For example, we hypothesize that microbial diversity is strongly controlled by the number of available electron donors and electron acceptors, rather than by limitations posed by environmental extremes such as low pH. In this case, both pH 0-1 and neutral Frasassi microbial communities will have lower diversity than a previously studied pH 0-1 acid mine drainage system where both iron and sulfur electron donors are available. The project also aims to identify biological and geological controls on sulfuric acid production (cave dissolution). Molecular biological methods will be used to quantify microbial populations, geochemical methods to document and monitor cave habitats and microbial cultures, and lipid and isotope-labeling methods to quantify biomass and identify autotrophic microorganisms in the cave communities.The project will involve 6 undergraduate thesis students and the development of an educational module to be incorporated into the highly successful Carleton College Geology Program in Italy. The work will generate young scientists with interdisciplinary training in geomicrobiology and publications that identify factors that control the structure and function of subsurface microbial communities responsible for sulfuric acid production and cave formation. More generally, understanding how microbial communities are assembled, and how these patterns of assembly affect the use of available resources, is a critical component of understanding the biogeochemistry of both ancient and present-day environments.