EAGER: Meta-gut Dynamics Influence Aquatic Ecosystem Processes

当动物排便或死亡时，它们将一部分肠道微生物转移到环境中，连同有机物，营养物质和代谢副产品，包括它们的粪便或尸体。微生物对这些输入物的分解可以改变生态系统的特征。在这个EAGER项目中，拟议的研究将测试这种耦合的肠道环境系统，即“元肠道”，是否允许来自鱼肠道的微生物群落在动物外部持续存在，并对生态系统功能产生更大的影响。河马是这个专门研究肯尼亚马拉河生态系统生态的团队这项研究的重点，马拉河拥有数千只河马，是世界著名的塞伦盖蒂国家公园野生动物唯一的永久水源。虽然环境微生物群落传统上被认为是生态系统功能的重要驱动因素，但动物肠道微生物可以直接显着影响生态系统功能的证明将代表我们对动物对生态系统过程影响的理解的范式转变。这项研究将增加我们对水生生态系统中有机物负荷影响的理解，以及在低氧条件下有机物分解和氮循环的微生物驱动因素，这些因素在一些水生生态系统中越来越普遍。该项目将在每年的补助金中培训一名博士后和2-3名本科生，并寻求扩大代表性不足的学生在科学领域的参与。这项研究的成果将被用于开发一个模块，为有河马设施的动物园，教育公众这些动物在构建河流生态系统中发挥的重要作用。拟议的研究将使用一种实验方法，该方法基于对马拉河河马的实地研究观察。河马聚集在沿着缓慢移动的水池中，在那里它们排泄出大量的有机物质，改变了水池的地球化学性质。以前的研究表明，高补贴池，大量河马输入和低冲洗率，可以成为缺氧。因此，这些水池发展出与河马肠道非常相似的微生物群落，这表明河马肠道微生物可能会在外部环境中持续存在。研究人员将在复制的溪流中生态系统中进行一项实验，使用微生物群落和生物地球化学反应的耦合高频采样，以测试河马肠道微生物是否可以在外部环境中持续存在和发挥作用，以及它们是否影响碳和营养循环。来自圈养动物设施的河马粪便将被添加到循环流中，从具有活性肠道微生物的新鲜粪便到无肠道微生物的灭菌粪便。河马肠道微生物的存在和活性将使用宏基因组学，元转录组学和代谢组学进行测量，因为围隔生态系统从有氧代谢过渡到厌氧代谢。这些测量将与水生生物地球化学、碳循环和氮代谢的详细测量相结合。一个随机种群模型将模拟河马肠道中的微生物如何生存并影响水池中的关键生态系统过程。除了对博士后和本科生进行培训外，这项研究的成果还将与肯尼亚的资源管理者和利益相关者分享，扩大对河马的生态作用及其对该地区水资源影响的理解。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

When animals defecate or die, they transfer a portion of their gut microbes to the environment, together with the organic matter, nutrients, and metabolic byproducts that comprise their feces or carcasses. Microbial decomposition of these inputs can change the characteristics of an ecosystem. In this EAGER project, the proposed research will test whether this coupled gut-environment system, the 'meta-gut', allows microbial communities from the gut of hippopotami to persist external to the animal and have a greater influence on ecosystem function. Hippos are the focus of this study by this team that specialized in the ecosystem ecology of the Mara River in Kenya, which has thousands of hippos and is the only permanent source of water for wildlife in the world-famous Serengeti National Park. Although environmental microbial communities are traditionally considered important drivers of ecosystem function, demonstration that animal gut microbes can significantly influence ecosystem function directly would represent a paradigm shift in our understanding of the influence of animals on ecosystem processes. This research will increase our understanding of the influence of organic matter loading in aquatic ecosystems, as well as microbial drivers of organic matter decomposition and nitrogen cycling under low oxygen conditions, which are increasingly common in some aquatic ecosystems. This project will train a postdoc and 2-3 undergraduate students in each year of the grant and seek to broaden the participation of underrepresented students in science. Products from this research will be used to develop a module for zoos that have hippo facilities to educate the general public about the important role these animals play in structuring river ecosystems.The proposed study will use an experimental approach based on observations from field research on hippos in the Mara River. Hippos aggregate in slow-moving pools along the river where they defecate large quantities of organic material that alter pool biogeochemistry. Previous research has shown that high subsidy pools, with large hippo inputs and low flushing rates, can become anoxic. As a result, these pools develop microbial communities that closely resemble the hippo gut, suggesting hippo gut microbes may persist in the external environment. Researchers will conduct an experiment in replicated stream mesocosms using coupled, high-frequency sampling of microbial communities and biogeochemical responses to test whether hippo gut microbes can persist and function in the external environment, and whether they influence carbon and nutrient cycling. Hippo feces from a captive animal facility will be added to recirculating streams across a gradient from fresh feces with active gut microbes to sterilized feces with no gut microbes. Presence and activity of microbes from the hippo gut will be measured using metagenomics, metatranscriptomics, and metabolomics, as the mesocosms transition from aerobic to anaerobic metabolism. These measurements will be coupled with detailed measurements on aquatic biogeochemistry, carbon cycling, and nitrogen metabolism. A stochastic population model will simulate how microbes from the hippo gut survive and influence key ecosystem processes in the pools. In addition to training the postdoc and undergraduate students, findings from this research will be shared with resource managers and stakeholders in Kenya, broadening the understanding of the ecological role of hippos and their influences on water resources in the region.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.