CAREER: Spatial and Temporal Dynamics of Nitrogen-Cycling Microbial Communities Across Physicochemical Gradients in the San Francisco Bay Estuary

“该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。“虽然氮（N）在许多海洋生态系统中是一种限制性的营养物质，从河口到公海，过量的N可能是极其有害的。富营养化在河口尤其令人关注，美国一半以上的河口都受到其影响。河口中有害的氮水平可以通过微生物氮循环中的紧密耦合过程来减少，包括硝化作用（氨的化学自养氧化为亚硝酸盐和硝酸盐）和反硝化作用（硝酸盐异化还原为N2气体）。事实上，耦合硝化-反硝化可以去除高达50%的外部溶解无机氮输入河口，从而降低富营养化的风险。尽管硝化和反硝化作用在河口系统的生态地球化学的重要性，令人惊讶的是，很少有人知道有关的微生物群落负责这些过程，或它们是如何受到关键的物理/化学因素的影响。研究人员将在旧金山弗朗西斯科湾-美国西海岸最大的河口-使用分子，生物地球化学和培养方法，探索如何分布，多样性，丰度和活动的关键N-循环社区的影响，在时间和空间尺度上的环境梯度。反硝化群落将使用编码关键反硝化酶亚硝酸盐还原酶的功能基因（nirK和nirS）进行研究，而编码氨单加氧酶亚基A（amoA）的基因将用于研究氨氧化细菌（AOB）和最近发现的氨氧化古菌（AOA）-地球上最普遍和丰富的原核生物群之一的成员，嗜温Crenarchaeota。分析沉积物从站点跨越一系列的物理和化学条件在海湾，季节性的过程中的几年，将是一个前所未有的机会，研究空间，物理/化学，和时间的影响，在这个大的，城市河口的净水器和氨氧化剂社区。与此同时，还将进行密集的培养工作，以编制一个新的河口浮游生物和氨氧化剂的文化收藏，目前几乎一无所知。综合起来看，这些互补的方法将有助于揭示复杂的物理/化学梯度如何影响关键河口氮循环群落的多样性和功能。更广泛的影响包括对潜在的氮循环群落如何进行批判性的理解。在旧金山弗朗西斯科湾河口，随着时间和空间的推移，循环微生物群落受到复杂和波动的环境梯度的影响，这应该转化为对生态和调节这些重要的生态化学过程在所有河口系统。此外，研究结果将通过几个关键的教育和推广活动进行交流和调查：（1）将开发和教授一个以旧金山弗朗西斯科湾为重点的社区级课程，作为理解大型河口的地球化学和社会重要性的模型系统;（2）海湾地区高中生物教师将参加为期4周的密集微生物学暑期课程;（3）为真实的（Redwood Environmental Academy of Learning）项目开发一个“微生物群落”模块，重点是在附近的Redwood高中对“继续”学生进行实践生态教学;（4）指导和培训研究生、本科生和高中生，他们将在未来5年内直接参与研究项目。

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."Although nitrogen (N) acts as a limiting nutrient in many marine ecosystems, from estuaries to the open ocean, N in excess can be extremely detrimental. Eutrophication is of particular concern in estuaries, with over half of the estuaries in the United States experiencing its effects. Harmful levels of N in estuaries can be diminished through tightly coupled processes in the microbial nitrogen cycle, including nitrification (chemoautotrophic oxidation of ammonia to nitrite and nitrate) and denitrification (the dissimilatory reduction of nitrate to N2 gas). In fact, coupled nitrification-denitrification can remove up to 50% of external dissolved inorganic nitrogen inputs to estuaries, thereby reducing the risk of eutrophication. Despite the biogeochemical importance of both nitrification and denitrification in estuarine systems, surprisingly little is known regarding the underlying microbial communities responsible for these processes, or how they are influenced by key physical/chemical factors. The investigators will work in San Francisco Bay - the largest estuary on the west coast of the United States - using molecular, biogeochemical and cultivation approaches to explore how the distribution, diversity, abundance, and activities of key N-cycling communities are influenced by environmental gradients over temporal and spatial scales. Denitrifying communities will be studied using functional genes (nirK and nirS) encoding the key denitrification enzyme nitrite reductase, while genes encoding ammonia monooxygenase subunit A (amoA) will be used to study both ammonia-oxidizing bacteria (AOB) and the recently-discovered ammonia-oxidizing archaea (AOA)- members of one of the most ubiquitous and abundant prokaryotic groups on the planet, the mesophilic Crenarchaeota. Analyzing sediments from sites spanning a range of physical and chemical conditions in the Bay, seasonally over the course of several years, will represent an unprecedented opportunity to examine spatial, physical/chemical, and temporal effects on both denitrifier and ammonia-oxidizer communities in this large, urban estuary. Concurrently, an intensive cultivation effort will also be undertaken, in order to compile a novel culture collection of estuarine denitrifiers and ammonia-oxidizers, for which virtually nothing is currently known. Taken together, these complimentary approaches will help reveal how complex physical/chemical gradients influence the diversity and functioning of key estuarine N-cycling communities over time and space.The broader impacts include obtaining a critical understanding of how underlying N-cycling microbial communities are influenced by complex and fluctuating environmental gradients over time and space in the San Francisco Bay estuary which should translate to insights into the ecology and regulation of these biogeochemically-important processes in all estuarine systems. In addition, results of the research will be communicated and investigated through several key educational and outreach activities: (1) a sophomore-level course to be developed and taught focused on San Francisco Bay as a model system for understanding the biogeochemical and societal importance of large estuaries; (2) Bay Area high school biology teachers will be targeted for a 4-week intensive microbiology summer course; (3) development of a 'microbial community' module to the REAL (Redwood Environmental Academy of Learning) Program, focused on the hands-on ecological teaching of 'continuation' students at nearby Redwood High School; and (4) mentoring and training of graduate, undergraduate, and high school students, who will be directly involved in the research project over the next 5 years.