COLLABORATIVE RESEARCH: The role of marine Crenarchaeota in nitrification and links among biogeochemical processes in the eastern tropical North Pacific and Gulf of California

硝化作用是通过亚硝酸盐将氨氧化为硝酸盐的两步过程，它通过改变N发生的形式，在全球氮(N)循环中起着关键作用，从而影响不同生物群体和生物地球化学过程对N的可及性和有效性，实际上，负责从海洋中固定和去除N的过程最终可能与硝化作用联系在一起。长期以来，人们一直认为硝化的第一步和限速步骤氨氧化仅限于细菌域内的几个群。然而，近年来氨氧化古菌（AOA）的发现严重挑战了我们对海洋硝化微生物生态学和生物地球化学的认识。在这个项目中，斯坦福大学和夏威夷大学马诺阿分校的研究人员将尝试定量地限制海洋绿原藻对海洋硝化作用的贡献，并研究加州湾（GOC）和热带北太平洋东部（ETNP）其他形式的氮代谢的联系。具体目标是：(1)在GOC和ETNP上部水柱（0-100m）的7个站点定量15n -铵氧化速率、细菌和古细菌amoA基因和转录本；(2)根据古菌膜脂对13C标记的碳酸氢盐的吸收，确定绿古菌是否主动固定无机碳（即自养）；(3)定量测定同一深度和站点的亚硝酸盐氧化速率和亚硝酸盐-氧化剂丰度；(4)将这些测量扩展到氧气最小带（OMZ）内的多个深度；(5)研究氨氧化古菌与GOC和ETNP OMZ中氮损失过程之间的潜在耦合；(6)通过将我们的研究结果与nsf资助的研究结合起来，将我们的研究结果置于更广阔的海洋学视角中，研究最终产生于OMZ的缺氮水的固氮作用。基于amoA丰度、基因表达、同位素标记的无机碳的主动固定以及与测量速率的相关性，研究人员预测海洋绿原藻将在氨氧化中发挥主导作用。在上部水柱和OMZ。他们还期望AOA与氧化（亚硝酸盐氧化）和还原性N代谢（如厌氧氨氧化）之间的代谢耦合将是明显的。就更广泛的影响而言，硝化作用在将有机物矿化与厌氧氮去除联系起来方面起着关键作用，该项目将提供有关硝化作用和潜在微生物群落如何受到关键环境梯度影响的关键信息，以及它们与其他n循环过程的联系。最终，这项多学科研究将为所有海洋系统中这一生物地球化学重要过程的生态学和调控提供见解。建议的研究有很好的教育机会，并且pi有成功指导和毕业硕士和/或博士学生的历史，并促进学生在国家会议上发表论文和演讲。本科、研究生和博士后教育将通过积极参与邮轮和邮轮后的分析，学生将与分子微生物生态学和稳定同位素生物地球化学专家合作，并学习最先进的实验和分析方法。

Nitrification, the two-step oxidation of ammonia to nitrate via nitrite, plays a critical role in the global nitrogen (N) cycle by changing the form in which N occurs, and consequently influencing the accessibility and availability of N to different groups of organisms and biogeochemical processes, indeed, the processes responsible for the fixation and removal of N from the ocean may ultimately be connected by nitrification. It has long been assumed that the first and rate-limiting step of nitrification, ammonia oxidation, is restricted to a few groups within the domain Bacteria. However, the recent discovery of ammonia-oxidizing Archaea (AOA) has seriously challenged our understanding of the microbial ecology and biogeochemistry of nitrification in the ocean. In this project, researchers at Stanford University and the University of Hawaii at Manoa will attempt to constrain quantitatively the contribution of marine Crenarchaeota to oceanic nitrification and investigate connections to other forms of nitrogen metabolism in the Gulf of California (GOC) and the eastern tropical North Pacific (ETNP). The specific objectives are to: (1) quantify 15N-ammonium oxidation rates, and bacterial and archaeal amoA genes and transcripts, at seven stations in the upper water column (0-100m) of the GOC and ETNP; (2) determine if Crenarchaeota are actively fixing inorganic carbon (i.e., autotrophic) based on uptake of 13C--labeled bicarbonate into archaeal membrane lipids; (3) quantify nitrite oxidation rates and nitrite-oxidizer abundances at the same depths and stations; (4) extend these measurements to multiple depths within the oxygen minimum zone (OMZ); (5) examine potential coupling between ammonia-oxidizing archaea and nitrogen loss processes in the OMZ of the GOC and ETNP, and (6) place our results in a broader oceanographic perspective by tying into NSF-funded work examining nitrogen fixation in N-deficient waters ultimately generated in OMZs. The researchers predict that marine Crenarchaeota will play a dominant role in ammonia oxidation-based on amoA abundance, gene expression, active fixation of isotopically-labeled inorganic carbon, and correlation to measured rates?in both the upper water column and OMZ. They also expect that metabolic coupling between AOA and both oxidative (nitrite oxidation) and reductive N metabolisms (e.g., anammox) will be apparent.With regard to broader impacts, nitrification plays a pivotal role in linking organic matter mineralization to anaerobic nitrogen removal, and this project will provide critical information regarding how nitrification and the underlying microbial communities are influenced by key environmental gradients, as well as their connections to other N-cycling processes. Ultimately, this multi-disciplinary study should provide insights into the ecology and regulation of this biogeochemically-important process in all marine systems. The proposed research has excellent educational opportunities, and the PIs have a history of successfully mentoring and graduating Masters and/or Ph.D. students and fostering student publications and presentations at national meetings. Undergraduate, graduate, and postdoctoral education will be furthered through active participation in the cruise and post-cruise analyses, where students will work collaboratively with experts in molecular microbial ecology and stable isotope biogeochemistry, and learn a spectrum of state-of-the-art experimental and analytical methods.