Enzyme‐level interconversion of nitrate and nitrite in the fall mixed layer of the Antarctic Ocean

Kemeny, Preston C.; Weigand, M. Alexandra; Zhang, Run; Carter, B. R.; Karsh, Kristen; Fawcett, Sarah E.; Sigman, Daniel M.

doi:10.1002/2015gb005350

Cited by 38 publications

(62 citation statements)

References 69 publications

(148 reference statements)

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“…We note that another possible source of apparent anaerobic NO 2 − oxidation results from the reversibility of the nitrite oxidoreductase enzyme by which aerobic nitrifiers living at the ODZ boundary are ephemerally stressed by the lack of O 2 [ Kemeny et al , ]. However, given the consistency of the O 2 and NO 2 − concentration profiles, this explanation suggested by natural abundance isotope data for light‐stressed nitrifiers in the high‐O 2 Southern Ocean surface requires more investigation within ODZs.…”

Section: Resultsmentioning

confidence: 99%

“…Two other noteworthy oxidants that have been explored in ODZs, iron and manganese, are also insufficient to support the observed rates [ Glass et al , ; Kondo and Moffett , ]. Nitrite oxidoreductase reversibility may also play a role [ Kemeny et al , ]. Cycling between nitrate reduction and nitrite reoxidation at the boundaries supplies ammonium to support greater rates of anammox relative to denitrification. The increased contribution of anammox at the boundaries may potentially arise due to very low O 2 concentrations having a differential inhibitory effect on the two N 2 production pathways [ Dalsgaard et al , ]. The ETSP nitrite maximum is produced and actively maintained by an imbalance among the microbial rates of nitrate reduction, anammox, anaerobic nitrite oxidation, and physics; however, the ultimate reason for this imbalance, either a kinetic or thermodynamic control to maximize energy yield, remains to be elucidated.…”

Section: Anaerobic Nitrogen Cycle Of the Etspmentioning

confidence: 99%

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Multiple metabolisms constrain the anaerobic nitrite budget in the Eastern Tropical South Pacific

Babbin

Peters

Mordy

et al. 2017

Global Biogeochemical Cycles

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The Eastern Tropical South Pacific is one of the three major oxygen deficient zones (ODZs) in the global ocean and is responsible for approximately one third of marine water column nitrogen loss. It is the best studied of the ODZs and, like the others, features a broad nitrite maximum across the low oxygen layer. How the microbial processes that produce and consume nitrite in anoxic waters interact to sustain this feature is unknown. Here we used 15 N-tracer experiments to disentangle five of the biologically mediated processes that control the nitrite pool, including a high-resolution profile of nitrogen loss rates. Nitrate reduction to nitrite likely depended on organic matter fluxes, but the organic matter did not drive detectable rates of denitrification to N 2 . However, multiple lines of evidence show that denitrification is important in shaping the biogeochemistry of this ODZ. Significant rates of anaerobic nitrite oxidation at the ODZ boundaries were also measured. Iodate was a potential oxidant that could support part of this nitrite consumption pathway. We additionally observed N 2 production from labeled cyanate and postulate that anammox bacteria have the ability to harness cyanate as another form of reduced nitrogen rather than relying solely on ammonification of complex organic matter. The balance of the five anaerobic rates measured-anammox, denitrification, nitrate reduction, nitrite oxidation, and dissimilatory nitrite reduction to ammonium-is sufficient to reproduce broadly the observed nitrite and nitrate profiles in a simple one-dimensional model but requires an additional source of reduced nitrogen to the deeper ODZ to avoid ammonium overconsumption.

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Section: Resultsmentioning

confidence: 99%

Section: Anaerobic Nitrogen Cycle Of the Etspmentioning

confidence: 99%

Multiple metabolisms constrain the anaerobic nitrite budget in the Eastern Tropical South Pacific

Babbin

Peters

Mordy

et al. 2017

Global Biogeochemical Cycles

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“…The close match in distribution and absolute rates of NO 3 − reduction and NO 2 − oxidation suggests that these processes are tightly coupled and lend some support to the hypothesis of Kemeny et al . [] that NO 2 − oxidizing bacteria might catalyze the interconversion of NO 3 − and NO 2 − under conditions unfavorable for their growth. We cannot determine the exact mechanism for NO 2 − oxidation in the ODZ from the model results in this study, but we do believe this warrants further examination.…”

Section: Discussionmentioning

confidence: 99%

Vertical modeling of the nitrogen cycle in the eastern tropical South Pacific oxygen deficient zone using high‐resolution concentration and isotope measurements

Peters

Babbin

Lettmann

et al. 2016

Global Biogeochemical Cycles

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Marine oxygen deficient zones (ODZs) have long been identified as sites of fixed nitrogen (N) loss. However, the mechanisms and rates of N loss have been debated, and traditional methods for measuring these rates are labor‐intensive and may miss hot spots in spatially and temporally variable environments. Here we estimate rates of heterotrophic nitrate reduction, heterotrophic nitrite reduction (denitrification), nitrite oxidation, and anaerobic ammonium oxidation (anammox) at a coastal site in the eastern tropical South Pacific (ETSP) ODZ based on high‐resolution concentration and natural abundance stable isotope measurements of nitrate (NO3−) and nitrite (NO2−). These measurements were used to estimate process rates using a two‐step inverse modeling approach. The modeled rates were sensitive to assumed isotope effects for NO3− reduction and NO2− oxidation. Nevertheless, we addressed two questions surrounding the fates of NO2− in the ODZ: (1) Is NO2− being primarily reduced to N2 or oxidized to NO3− in the ODZ? and (2) what are the contributions of anammox and denitrification to NO2− removal? Depth‐integrated rates from the model suggest that 72–88% of the NO2− produced in the ODZ was oxidized back to NO3−, while 12–28% of NO2− was reduced to N2. Furthermore, our model suggested that 36–74% of NO2− loss was due to anammox, with the remainder due to denitrification. These model results generally agreed with previously measured rates, though with a large range of uncertainty, and they provide a long‐term integrated view that compliments incubation experiments to obtain a broader picture of N cycling in ODZs.

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“…These models have generally interpreted the nitrate reduction and nitrite oxidation as processes carried out by different groups of organisms acting in concert. However, an alternative explanation for the observed δ 15 N NO 3 and δ 15 N NO 2 distributions includes rapid interconversion between nitrate and nitrite within a single organism [43,65]. It is likely that other factors are affecting the isotopic distributions such as isopycnal mixing or spatio-temporal separation of processes caused by O 2 fluctuations or organic matter supply.…”

Section: (C) Rayleigh Model Versus Time-dependent Modelmentioning

confidence: 99%

Nitrite isotopes as tracers of marine N cycle processes

Casciotti¹

2016

Phil. Trans. R. Soc. A.

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Enzyme‐level interconversion of nitrate and nitrite in the fall mixed layer of the Antarctic Ocean

Abstract: In the Southern Ocean, the nitrogen (N) isotopes of organic matter and the N and oxygen (O) isotopes of nitrate (NO 3 À ) have been used to investigate NO 3 À assimilation and N cycling in the summertime period of phytoplankton growth, both today and in the past.

Cited by 38 publications

References 69 publications

Multiple metabolisms constrain the anaerobic nitrite budget in the Eastern Tropical South Pacific

Multiple metabolisms constrain the anaerobic nitrite budget in the Eastern Tropical South Pacific

Vertical modeling of the nitrogen cycle in the eastern tropical South Pacific oxygen deficient zone using high‐resolution concentration and isotope measurements

Nitrite isotopes as tracers of marine N cycle processes

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