Nitrogen fixation: A poorly understood process along the freshwater‐marine continuum

Marcarelli, Amy; Fulweiler, Robinson W.; Scott, J. Thad

doi:10.1002/lol2.10220

Cited by 33 publications

(14 citation statements)

References 83 publications

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“…4C), which are similarly to previous reports (Halm et al, 2009;Marcarelli & Wurtsbaugh, 2006Rahav et al, 2022). Note, data on N 2 xation rates in freshwater environments is highly limited (Marcarelli et al, 2022). Normalizing these rates to the number of diazotrophs detected by immunolabeling ow cytometry (DA) resulted in N 2 xation per cell, ranging between 88 attomole N cell − 1 at the Mediterranean Sea to 0.3 attomole N cell − 1 at the Sea of Galilee Lake (Fig.…”

Section: Evaluating the Abundance Of Diazotrophs In Aquatic Environmentssupporting

confidence: 87%

Quantification of Aquatic Unicellular Diazotrophs by Immunolabeled Flow Cytometry

Zeev

Geisler

Siebner

et al. 2022

Preprint

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Unicellular diazotrophs are recognized as important contributors to the aquatic nitrogen cycle. Yet, quantifying the number of aquatic diazotrophs, especially the unicellular fraction, is highly challenging and relies mostly on microscopical and molecular approaches. In this study a new method was developed to quantify unicellular diazotrophs by combining immunolabeling the nitrogenase enzyme and flow cytometry. The quantification method was initially developed using a diazotrophic monoculture (Vibrio natriegens) and verified by different controls as well as various auxiliary approaches such as N2 fixation and confocal laser scanning microscopy. It was evident that only 15–20% of the total number of V. natriegens cells have synthesized the nitrogenase enzyme, even though the media was anaerobic, and N limited. This approach was further tested on field samples collected from marine and freshwater environments. It was found that the number of unicellular diazotrophs sampled from the Mediterranean Sea comprised 0.1% of the total bacteria, while 4.7% along the Jordan River. Nevertheless, N2 fixation per cell was highest in the Mediterranean Sea (~ 90 attmole N cell− 1 d− 1), while lower in the lake and the river (1.4 to 0.3 attmole N cell− 1 d− 1, respectively). Following the above, it is expected that this direct quantification approach will provide new insights on the number and specific contribution of unicellular diazotrophs to total N2 fixation in marine and freshwater environments.

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Section: Evaluating the Abundance Of Diazotrophs In Aquatic Environmentssupporting

confidence: 87%

Quantification of Aquatic Unicellular Diazotrophs by Immunolabeled Flow Cytometry

Zeev

Geisler

Siebner

et al. 2022

Preprint

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“…Still, these methods cannot measure NCD-specific N 2 fixation rates unambiguously. Thus, despite of the widespread distribution and activity of NCDs, their contribution to aquatic nitrogen cycling remains elusive (see reviews: Riemann et al, 2010 ; Bombar et al, 2016 ; Moisander et al, 2017 ; Benavides et al, 2018a ; Marcarelli et al, 2022 ).…”

Section: Introductionmentioning

confidence: 99%

Planktonic Aggregates as Hotspots for Heterotrophic Diazotrophy: The Plot Thickens

et al. 2022

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Biological dinitrogen (N2) fixation is performed solely by specialized bacteria and archaea termed diazotrophs, introducing new reactive nitrogen into aquatic environments. Conventionally, phototrophic cyanobacteria are considered the major diazotrophs in aquatic environments. However, accumulating evidence indicates that diverse non-cyanobacterial diazotrophs (NCDs) inhabit a wide range of aquatic ecosystems, including temperate and polar latitudes, coastal environments and the deep ocean. NCDs are thus suspected to impact global nitrogen cycling decisively, yet their ecological and quantitative importance remain unknown. Here we review recent molecular and biogeochemical evidence demonstrating that pelagic NCDs inhabit and thrive especially on aggregates in diverse aquatic ecosystems. Aggregates are characterized by reduced-oxygen microzones, high C:N ratio (above Redfield) and high availability of labile carbon as compared to the ambient water. We argue that planktonic aggregates are important loci for energetically-expensive N2 fixation by NCDs and propose a conceptual framework for aggregate-associated N2 fixation. Future studies on aggregate-associated diazotrophy, using novel methodological approaches, are encouraged to address the ecological relevance of NCDs for nitrogen cycling in aquatic environments.

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“…Corresponding N 2 fixation rates from these samples were between 0.2 to 1.2 nmole N L -1 (Figure 4C), which are in similar ranges to previous reports (Halm et al, 2009; Marcarelli & Wurtsbaugh, 2006, 2009; Rahav et al, 2022). Note, data on N 2 fixation rates in freshwater environments is still limited (Marcarelli et al, 2022). Normalizing these rates to the number of diazotrophs detected by immunolabeling flow cytometry resulted in N 2 fixation per cells that ranged between 0.3-88 attomole N cell -1 .…”

Section: Resultsmentioning

confidence: 99%

Quantification of Aquatic Unicellular Diazotrophs by Immunolabeled Flow Cytometry

Geisler

Siebner

Rahav

et al. 2022

Preprint

View full text Add to dashboard Cite

Quantifying the number of aquatic diazotrophs is highly challenging and relies mainly on microscopical approaches and/or molecular tools that are based on nif genes. However, it is still challenging to count diazotrophs, especially the unicellular fraction, despite their significant contribution to the aquatic nitrogen cycle. In this study a new method was developed to quantify unicellular diazotrophs by immunolabeling the nitrogenase enzyme followed by identification and quantification via flow cytometry. The new quantification method was initially developed using a diazotrophic monoculture (Vibrio natriegens) and verified by various auxiliary approaches. It was found that only 15-20% of the total number of V. natriegens cells have synthesized the nitrogenase enzyme, even though the media was anaerobic, and N limited. This approach was further tested in samples from marine and freshwater environments. It was found that the ratio of diazotrophs to total bacteria was 0.1% in the Mediterranean Sea, while 4.7% along the Jordan River. In contrast, the specific N2 fixation per unicellular diazotrophs was highest in the Mediterranean Sea (88 attomole N cell-1 d-1) while the total N2 fixation rates were lowest in the lake and the river (0.2 nmole N L-1 d-1). Overall, we expect that this direct quantification approach will provide new insights on the number and contribution of unicellular diazotrophs to total N2 fixation in marine and freshwater environments under various conditions.

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Nitrogen fixation: A poorly understood process along the freshwater‐marine continuum

Cited by 33 publications

References 83 publications

Quantification of Aquatic Unicellular Diazotrophs by Immunolabeled Flow Cytometry

Quantification of Aquatic Unicellular Diazotrophs by Immunolabeled Flow Cytometry

Planktonic Aggregates as Hotspots for Heterotrophic Diazotrophy: The Plot Thickens

Quantification of Aquatic Unicellular Diazotrophs by Immunolabeled Flow Cytometry

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