Separating the efflux and influx components of net nitrate uptake by Synechococcus R2 under steady-state conditions

Georgia, Shearer; Schneider, Julie D.; Kohl, Daniel H.

doi:10.1099/00221287-137-5-1179

Cited by 33 publications

(5 citation statements)

References 14 publications

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“…Previous studies have shown that variations in cellularlevel isotope effect expression is imparted by changes to the ratio of cellular substrate uptake to efflux (Shearer et al 1991;Needoba et al 2004;Granger et al 2008). However, it has been shown in P. stutzeri that uptake and efflux of nitrite are fast compared to the rate of nitrite reduction (Bryan et al 1983).…”

Section: Enzyme-level Differencesmentioning

confidence: 99%

Nitrogen and oxygen isotopic fractionation during microbial nitrite reduction

Martin

Casciotti

2016

Limnology & Oceanography

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Microbial nitrite reduction plays an important role in the nitrogen cycle, producing the first gaseous product in the denitrification pathway. The role of nitrite reduction in the environment can be assessed using stable isotope measurements of nitrite. Here, we present estimates for nitrogen (N) and oxygen (O) isotope fractionation during nitrite reduction catalyzed by copper‐containing nitrite reductase (Cu‐NIR) and cytochrome cd1‐containing nitrite reductase (Fe‐NIR). A Rayleigh fractionation model was used to calculate the N and O isotope effects, 15ε and 18ε respectively, from time‐course measurements of nitrite concentration and isotopic composition in batch culture experiments. For three strains of denitrifier carrying the Cu‐NIR, 15ε = 22 ± 2‰ and 18ε = 2 ± 2‰ (95% confidence interval). For three strains of denitrifier carrying the Fe‐NIR, 15ε = 8 ± 2 and 18ε = 6 ± 2‰ (95% confidence interval). These isotope effects for nitrite reduction are significantly different from each other. Furthermore, 15ε and 18ε do not show a 1 : 1 relationship, as has been assumed. The difference between the isotope effects for these two families of enzymes is likely due to a mechanical difference in how the enzymes bind nitrite. The Cu‐NIR binds to both O atoms and the Fe‐NIR only binds to the N, allowing either NO bond to be cleaved and imparting a larger isotope effect for O than for the Cu‐NIR. Utilizing these new N isotope effects for nitrite reduction in oxygen minimum zone N cycle models results in higher rates of nitrite oxidation than previously modeled.

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Section: Enzyme-level Differencesmentioning

confidence: 99%

Nitrogen and oxygen isotopic fractionation during microbial nitrite reduction

Martin

Casciotti

2016

Limnology & Oceanography

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“…In particular, noted that among monocultures of four phytoplankton strains, two diatoms and a prymnesiophyte showed higher N isotope effects in light-limited vs. high-light cultures, whereas one diatom species exhibited no increase in 15 ε at low light. Speciesspecific differences in 15 ε as well as intra-species differences in 15 ε have been attributed to variation in the expression of the enzymatic isotope effect imposed by nitrate reductase, which is determined by the ratio of NO − 3 effluxing out of the cell relative to its uptake (Shearer et al, 1991;Granger et al, 2004;. The intrinsic N (and O) isotope effect(s) of the eukaryotic assimilatory NO − 3 reductase in vitro has been estimated to be ∼27‰ (Karsh et al, 2012), whereas data on the N or O isotope effects imparted on NO − 3 during its active uptake at the cell surface indicate that they range between minor (up to 2‰; Karsh et al, 2013) and undetectable (Granger et al, 2010).…”

Section: Growth Dynamics At High and Low Lightmentioning

confidence: 99%

“…N and O isotope discrimination of NO − 3 during its assimilation is thus incurred dominantly during intracellular reduction by nitrate reductase. However, the enzymatic 15 N-enrichment that is transmitted to the external medium through cellular efflux of the internal NO − 3 pool and the cellular-level isotope effect (i.e., the expression of the isotope fractionation in the external medium) depends on the ratio of uptake to efflux (i.e., "efflux model"; Shearer et al, 1991;Granger et al, 2004;, which may vary with changing physiological and/or environmental conditions.…”

Section: Growth Dynamics At High and Low Lightmentioning

confidence: 99%

Coupled nitrate N and O stable isotope fractionation by a natural marine plankton consortium

et al. 2015

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The stable nitrogen (N) and oxygen (O) nitrification. Differences in irradiance in the fall incubations resulted in slightly reduced nitrate consumption at low light but had no distinguishable impact on the N isotope effect ( 15 ε) associated with NO − assimilation, which ranged between 5 and 8‰. The 3 late-summer community incubations, in contrast, showed significantly reduced growth rates at low light and more elevated 15 ε of 11.9 ± 0.4‰, compared to 8.4 ± 0.3‰ at high-light conditions. The seasonal differences could reflect physiological adaptations of the fall plankton community to reduced irradiance, such that their incubation at low light did not elicit the increase in proportional cellular nitrate efflux required to raise the isotope effect. In both the fall and summer incubations, the ratio of the coincident rises in the 15 δ N and 18 δ O of NO − was comparable to previous monoculture phytoplankton experiments, δ O: 15 δ N is expected if nitrification occurs concomitantly with nitrate assimilation. The lack of such decoupling is best explained by the absence of significant nitrification in any of our study's treatments, an interpretation supported by our inability to identify any tracer 15 N and 18 O uptake into the NO − pool in the late-summer community incubations.

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“…The efflux of NO − 3 from root to soil or the subsequent transport of NO − 3 within plants is not expected to discriminate 15 N as with the entry of soil NO − 3 into root cells (Mariotti et al, 1982; Shearer et al, 1991). This can be attributed to that the diffusion of NO − 3 through the membrane carriers of plant cells does not cause bonding breakage or consumption (Werner and Schmidt, 2002; Granger et al, 2004; Needoba et al, 2004).…”

Section: Isotopic Systematics Of No−3 In Plantsmentioning

confidence: 99%

Nitrate dynamics in natural plants: insights based on the concentration and natural isotope abundances of tissue nitrate

et al. 2014

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The dynamics of nitrate (NO−3), a major nitrogen (N) source for natural plants, has been studied mostly through experimental N addition, enzymatic assay, isotope labeling, and genetic expression. However, artificial N supply may not reasonably reflect the N strategies in natural plants because NO−3 uptake and reduction may vary with external N availability. Due to abrupt application and short operation time, field N addition, and isotopic labeling hinder the elucidation of in situ NO−3-use mechanisms. The concentration and natural isotopes of tissue NO−3 can offer insights into the plant NO−3 sources and dynamics in a natural context. Furthermore, they facilitate the exploration of plant NO−3 utilization and its interaction with N pollution and ecosystem N cycles without disturbing the N pools. The present study was conducted to review the application of the denitrifier method for concentration and isotope analyses of NO−3 in plants. Moreover, this study highlights the utility and advantages of these parameters in interpreting NO−3 sources and dynamics in natural plants. We summarize the major sources and reduction processes of NO−3 in plants, and discuss the implications of NO−3 concentration in plant tissues based on existing data. Particular emphasis was laid on the regulation of soil NO−3 and plant ecophysiological functions in interspecific and intra-plant NO−3 variations. We introduce N and O isotope systematics of NO−3 in plants and discuss the principles and feasibilities of using isotopic enrichment and fractionation factors; the correlation between concentration and isotopes (N and O isotopes: δ18O and Δ17O); and isotope mass-balance calculations to constrain sources and reduction of NO−3 in possible scenarios for natural plants are deliberated. Finally, we offer a preliminary framework of intraplant δ18O-NO−3 variation, and summarize the uncertainties in using tissue NO−3 parameters to interpret plant NO−3 utilization.

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Separating the efflux and influx components of net nitrate uptake by Synechococcus R2 under steady-state conditions

Cited by 33 publications

References 14 publications

Nitrogen and oxygen isotopic fractionation during microbial nitrite reduction

Nitrogen and oxygen isotopic fractionation during microbial nitrite reduction

Coupled nitrate N and O stable isotope fractionation by a natural marine plankton consortium

Nitrate dynamics in natural plants: insights based on the concentration and natural isotope abundances of tissue nitrate

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