Nitrite Oxidation in Oxygen Minimum Zones

最低氧区中的亚硝酸盐氧化

• 批准号: 1946516
• 负责人: Bess Ward
• 金额: $ 75.25万
• 依托单位: Princeton University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-03-01 至 2025-02-28
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1946516&HistoricalAwards=false
• 关键词: Nitrite; Oxidation; Oxygen; Minimum; Zones

This research is grounded in the fundamental role of nitrogen in limiting production in the ocean. Nitrite is a pivotal compound in the nitrogen cycle: it can be oxidized to nitrate, and thus retained as an available nutrient, or it can be reduced to dinitrogen gas, and thus lost from the bioavailable nitrogen pool. Oxidation of nitrite by nitrite oxidizing bacteria (NOB) is the only biological pathway by which nitrate is produced, and all known NOB require oxygen for life. The reduction pathway is also carried out by microbes, in this case, bacteria that thrive only in the absence of oxygen. In previous experiments, however, both oxidation and reduction of nitrite were detected in the same samples from ocean waters in the absence of oxygen. We will investigate three explanations for the apparent oxidation of nitrite in the absence of oxygen on a research cruise to the low oxygen waters off the coast of Peru: 1) The presence of unknown kinds of NOB that do not require oxygen; 2) a new reaction called dismutation, which is possible but never detected in nature; 3) an artifact associated with oxygen stress in NOB. This research could lead to discovery of novel mechanisms and or novel organisms that determine the fate of nitrite and the availability of nitrogen to support primary production in the long run. This project will advance discovery and understanding while promoting teaching, training and learning by providing opportunities for Princeton students to get involved in and have hands on experience in research in the lab and potentially at sea. Both undergraduate and graduate students will participate in the research through internships and field experiences. We will also integrate our work at sea into teaching in the classroom via videos and assignments based on data collected during the cruise.Nitrite oxidation is the only known biological process that produces nitrate, which comprises the largest fixed nitrogen reservoir in the ocean. Nitrite oxidation is carried out by nitrite oxidizing bacteria (NOB), and all known species are obligate aerobes. Nitrite reduction to N2 occurs in multiple microbial pathways, generally under anoxic conditions. Despite their apparent incompatibility regarding oxygen, both processes are detected in the low oxygen or anoxic waters of oxygen minimum zones (OMZs). Thus, the fate of nitrite in OMZs has implications for the global fixed N budget. Nitrite oxidation is detected at high rates in essentially zero oxygen water in the most oxygen depleted depth intervals in OMZ regions, which suggests that some nitrite oxidizers might possess anaerobic metabolic capabilities. Nitrite disproportionation (or dismutation), in which nitrite is simultaneously oxidized to nitrate and reduced to N2, is a thermodynamically favorable reaction, which would link the two processes in one organism – but it has never been observed in nature. The research proposed here will address two big questions about nitrite in the ocean: 1) How does anaerobic nitrite oxidation work? 2) What determines the fate of nitrite? The experimental approach will investigate three possible explanations for anaerobic nitrite oxidation: 1) Nitrite is oxidized to nitrate by different clades of NOB, which exhibit different tolerances/requirements for oxygen; 2) Nitrite dismutation, also performed by NOB, partially explains the cooccurrence of oxidation and reduction of nitrite; 3) Apparently anaerobic nitrite oxidation is indeed biologically mediated but does not always represent net production of nitrate from nitrite; rather it results from isotopic equilibration during enzyme-catalyzed interconversion of nitrite and nitrate. These questions will be addressed by performing a suite of 15N-tracer incubations at stations located within and outside of one of the major OMZs in the ocean, the Eastern Tropical South Pacific. The dependence of the rate processes on oxygen concentrations will be determined, and the composition of the microbial assemblages will be assessed in order to determine whether different microbial components are involved under different environmental conditions. The expression of genes involved in oxidation/reduction/ respiratory metabolisms at low oxygen concentrations will be measured across oxygen gradients and in oxygen manipulations to identify their potential role in supporting “anaerobic” nitrite oxidation. The possibility that the apparently anaerobic nitrite oxidation is due to an enzyme level interconversion between nitrite and nitrate, which does not lead to net nitrate production and is not linked to growth of nitrite oxidizing bacteria, will also be investigated.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.

这项研究基于氮在限制海洋生产中的基本作用。亚硝酸盐在氮循环中是一种关键化合物：它可以被氧化为硝酸盐，因此可以保留为可用的营养素，也可以将其减少为二氮气，从而从生物利用的氮池中丢失。亚硝酸盐氧化细菌（NOB）对亚硝酸盐的氧化是唯一产生硝酸盐的生物学途径，并且所有已知的NOB都需要生命的氧气。还原途径还通过微生物进行，在这种情况下，仅在没有氧气的情况下就蓬勃发展。然而，在先前的实验中，在没有氧气的情况下，在海水中的相同样品中检测到亚硝酸盐的氧化和还原。我们将研究三个解释，即在研究巡游中没有氧气前往秘鲁沿海低氧水域上的氧气明显氧化的三种解释：1）存在不需要氧气的未知类型的NOB； 2）一种称为DIMSOUNT的新反应，在本质上是可能但从未发现的； 3）与NOB中的氧气应激相关的伪影。这项研究可能导致发现新的机制和 /或新的生物体，这些机制决定了亚硝酸盐的命运以及从长远来看氮的可用性来支持一级生产。该项目将通过为普林斯顿学生提供参与并获得实验室研究经验的机会，在促进教学，培训和学习的同时提高发现和理解。本科生和研究生都将通过实习和实地经验参加研究。我们还将通过基于巡航过程中收集的数据将海上的工作整合到教室里的教学中。硝酸盐氧化是产生硝酸盐的唯一已知的生物学过程，硝酸盐包括最大的固定亚硝酸盐氧化是由亚硝酸盐氧化的，是通过硝酸盐氧化细菌（NOB）和所有已知种类的含量。亚硝酸盐还原至N2发生在多种微生物途径中，通常在缺氧条件下。尽管它们在氧气方面明显不相容，但在低氧或氧最小区（OMZ）的低氧或缺氧水中都检测到这两个过程。这是OMZ中亚硝酸盐的命运对全球固定N预算的影响。在OMZ区域中最大的氧气深度间隔中，以高速度为零的氧气中检测到亚硝酸盐氧化，这表明某些亚硝酸盐氧化剂可能具有厌氧代谢能力。亚硝酸盐的比例（或丢弃）是一种热力学上有利的反应，其中亚硝酸盐被简单地氧化为硝酸盐并将其降低到N2，这会将一个生物体中的两个过程联系起来，但在自然界中从未观察到。这里提出的研究将解决有关海洋中亚硝酸盐的两个大问题：1）厌氧亚硝酸盐氧化如何起作用？ 2）是什么决定了亚硝酸盐的命运？实验方法将研究厌氧亚硝酸盐氧化的三个可能的解释：1）亚硝酸盐被不同的NOB核酸盐氧化以硝酸盐，这些NOB的不同进化枝暴露了氧气的不同耐受性/需求； 2）not的一部分散布，部分解释了亚硝酸盐的氧化和还原的同时发生； 3）显然，厌氧亚硝酸盐的氧化确实是生物学介导的，但并不总是代表硝酸盐的硝酸盐净产生；相反，它是由于亚硝酸盐和硝酸盐的酶催化相互转换过程中的同位素当量引起的。这些问题将通过在东部热带南太平洋的海洋主要OMZ之一内外进行15N追踪孵化来解决。将确定速率过程对氧浓度的依赖性，并将评估微生物组合的组成，以确定在不同的环境条件下是否涉及不同的微生物成分。将在低氧浓度和氧气操作中测量参与低氧浓度下氧化/还原/呼吸代谢的基因的表达，以确定支持“厌氧”亚硝酸盐氧化方面的潜在作用。显然是由于亚硝酸盐和硝酸盐之间的酶水平相互转换引起的可能性，并不会导致硝酸盐净产量，并且与亚硝酸盐氧化细菌的增长无关，这也将得到研究，这也将得到研究。该奖项也将被调查。该奖项反映了NSF的智力和范围的启发性，其智力是依据的依据，其依据是依据的依据，其依据是依据的依据。审查标准。

项目成果

Database of nitrification and nitrifiers in the global ocean

• DOI: 10.5194/essd-15-5039-2023
• 发表时间: 2023-11
• 期刊: Earth System Science Data
• 影响因子: 11.4
• 作者: Weiyi Tang;B. Ward;Michael Beman;Laura Bristow;Darren Clark;Sarah Fawcett;C. Frey;François Fripiat;G. Herndl;Mhlangabezi Mdutyana;F. Paulot;Xuefeng Peng;A. Santoro;T. Shiozaki;E. Sintes;Charles Stock;Xin Sun;X. Wan;Min N. Xu;Yao Zhang

Nitrite Oxidation Across the Full Oxygen Spectrum in the Ocean

• DOI: 10.1029/2022gb007548
• 发表时间: 2023-03
• 期刊: Global Biogeochemical Cycles
• 影响因子: 5.2
• 作者: Xin Sun;C. Frey;B. Ward

Controls on nitrite oxidation in the upper Southern Ocean: insights from winter kinetics experiments in the Indian sector

• DOI: 10.5194/bg-19-3425-2022
• 发表时间: 2022-07-20
• 期刊: BIOGEOSCIENCES
• 影响因子: 4.9
• 作者: Mdutyana, Mhlangabezi;Marshall, Tanya;Fawcett, Sarah E.
• 通讯作者: Fawcett, Sarah E.