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.

这项研究的基础是氮在限制海洋产量方面的基本作用。 亚硝酸盐是氮循环中的关键化合物：它可以被氧化为硝酸盐，从而作为可用营养物保留下来，或者它可以被还原为氮气，从而从生物可利用氮库中损失。亚硝酸盐氧化细菌 (NOB) 氧化亚硝酸盐是产生硝酸盐的唯一生物途径，所有已知的 NOB 的生命都需要氧气。 还原途径也是由微生物执行的，在这种情况下，细菌只在没有氧气的情况下才能繁殖。 然而，在之前的实验中，在没有氧气的情况下，在来自海水的相同样品中检测到了亚硝酸盐的氧化和还原。我们将在前往秘鲁沿海低氧水域的研究航行中，研究在缺氧情况下亚硝酸盐明显氧化的三种解释：1）存在不需要氧气的未知种类的 NOB； 2）一种称为歧化的新反应，这种反应是可能的，但在自然界中从未被发现； 3) NOB 中与氧应激相关的伪影。 这项研究可能会发现新的机制和/或新的生物体，这些机制和/或新的生物体决定了亚硝酸盐的命运以及从长远来看支持初级生产的氮的可用性。该项目将为普林斯顿大学的学生提供参与实验室和潜在的海上研究并获得实践经验的机会，从而促进发现和理解，同时促进教学、培训和学习。 本科生和研究生都将通过实习和现场经验参与研究。我们还将根据航行期间收集的数据，通过视频和作业将我们的海上工作融入到课堂教学中。亚硝酸盐氧化是唯一已知的产生硝酸盐的生物过程，硝酸盐构成了海洋中最大的固定氮库。亚硝酸盐氧化是由亚硝酸盐氧化细菌（NOB）进行的，所有已知的物种都是专性需氧菌。亚硝酸盐还原成 N2 发生在多种微生物途径中，通常是在缺氧条件下。尽管它们在氧气方面明显不相容，但这两个过程都在最低氧区 (OMZ) 的低氧或缺氧水中检测到。 因此，亚硝酸盐在 OMZ 中的命运对全球固定氮预算具有影响。在 OMZ 区域最缺氧的深度区间，在基本为零氧的水中以很高的速率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。 亚硝酸盐歧化（或歧化）是一种热力学上有利的反应，其中亚硝酸盐同时被氧化为硝酸盐并被还原为氮气，它将在一个有机体中将这两个过程联系起来，但在自然界中从未观察到过这种反应。 这里提出的研究将解决海洋中亚硝酸盐的两个大问题：1）厌氧亚硝酸盐氧化是如何进行的？ 2) 亚硝酸盐的命运由什么决定？该实验方法将研究厌氧亚硝酸盐氧化的三种可能的解释：1）亚硝酸盐被不同的NOB进化枝氧化成硝酸盐，这些进化枝对氧气表现出不同的耐受性/要求； 2）亚硝酸盐歧化，也由NOB进行，部分解释了亚硝酸盐氧化和还原的同时发生； 3) 显然，厌氧亚硝酸盐氧化确实是生物介导的，但并不总是代表亚硝酸盐净产生硝酸盐；相反，它是酶催化亚硝酸盐和硝酸盐相互转化过程中同位素平衡的结果。 这些问题将通过在东热带南太平洋海洋主要 OMZ 内外的站点进行一套 15N 示踪剂孵化来解决。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，以确定不同的环境条件下是否涉及不同的微生物成分。将在氧梯度和氧操作中测量低氧浓度下参与氧化/还原/呼吸代谢的基因的表达，以确定它们在支持“厌氧”亚硝酸盐氧化中的潜在作用。还将调查明显厌氧亚硝酸盐氧化是由于亚硝酸盐和硝酸盐之间的酶水平相互转化引起的可能性，这种转化不会导致净硝酸盐产生，也与亚硝酸盐氧化细菌的生长无关。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响进行评估，被认为值得支持。 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.