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Related Concept Videos

Inorganic Nitrogen Assimilation01:22

Inorganic Nitrogen Assimilation

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Nitrogen is an essential element in biological systems, forming a crucial component of proteins, nucleic acids, and other cellular constituents. Many bacteria and archaea acquire nitrogen in the form of nitrate (NO₃⁻) or ammonia (NH₃), which are then assimilated into biomolecules through specific enzymatic pathways.Assimilatory Nitrate ReductionWhen nitrate enters the cell, it undergoes a two-step reduction process known as assimilatory nitrate reduction. Initially, the enzyme...
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Carbon-dioxide Fixation01:28

Carbon-dioxide Fixation

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Carbon dioxide fixation in prokaryotes enables the assimilation of inorganic carbon into organic molecules, supporting biosynthetic pathways, sustaining ecosystems, and contributing to the global carbon cycle. It also has industrial applications in carbon capture and bioproduct synthesis. Autotrophic organisms rely on this process to utilize CO₂ as a carbon source in diverse environments.The Calvin CycleThe Calvin cycle is the most widespread carbon fixation mechanism, primarily used by...
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Metabolism of Chemolithotrophs01:15

Metabolism of Chemolithotrophs

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Chemolithotrophs are microorganisms that obtain energy by oxidizing inorganic molecules such as hydrogen gas (H₂), ammonia (NH₃), reduced sulfur compounds (H₂S, S²⁻), and ferrous iron (Fe²⁺). Unlike heterotrophic organisms that rely on organic carbon, chemolithotrophs transfer electrons from these inorganic donors to the electron transport chain (ETC), generating a proton motive force (PMF) that drives ATP synthesis through oxidative phosphorylation.
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Overview of Nitrogen Metabolism01:20

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Nitrogen is a very important element for life because it is a major constituent of proteins and nucleic acids. It is a macronutrient, and in nature, it is recycled from organic compounds and stored in the form of  ammonia, ammonium ions, nitrate, nitrite, or  nitrogen gas by many metabolic processes. Many of these metabolic processes are carried out only by prokaryotes.
The largest pool of nitrogen available in the terrestrial ecosystem is gaseous nitrogen (N2) from the air, but this...
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The Nitrogen Cycle01:49

The Nitrogen Cycle

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Nitrogen atoms, present in all proteins and DNA, are recycled between abiotic and biotic components of the ecosystem. However, the primary form of nitrogen on Earth is nitrogen gas, which cannot be used by most animals and plants. Thus, nitrogen gas must first be converted into a usable form by nitrogen-fixing bacteria before it can be cycled through other living organisms. The use of nitrogen-containing fertilizers and animal waste products in human agriculture has greatly influenced the...
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Overview of Metabolism01:40

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Living cells constantly carry out various chemical reactions which are necessary for their proper functioning. These reactions are interlinked to one another via multiple pathways. The collection of these chemical reactions is known as metabolism.
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Updated: Dec 21, 2025

Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4+/15NH4+ Analyses via Sequential Conversion to N2O
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Changing perspectives in marine nitrogen fixation.

Jonathan P Zehr1, Douglas G Capone2

  • 1Department of Ocean Sciences, University of California, Santa Cruz, CA 95003, USA. zehrj@ucsc.edu capone@usc.edu.

Science (New York, N.Y.)
|May 16, 2020
PubMed
Summary
This summary is machine-generated.

Marine nitrogen fixation, converting atmospheric nitrogen (N2) to ammonia, is vital for ocean life. New research reveals diverse microbes and adaptations, transforming our understanding of this crucial process in the global nitrogen cycle.

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Area of Science:

  • Marine biology
  • Biogeochemistry
  • Microbial ecology

Background:

  • Nitrogen fixation (N2 to ammonia) is essential for marine productivity but challenging to study.
  • Recent advances integrate molecular, genomic, isotopic, and modeling techniques.
  • This has revealed novel diazotrophs and physiological adaptations in the ocean.

Purpose of the Study:

  • To revolutionize the understanding of marine nitrogen fixation.
  • To explore the role of diazotrophs in the global nitrogen cycle.
  • To investigate the impact of anthropogenic changes on marine N2 fixation.

Main Methods:

  • Field studies over decades.
  • Molecular biological and genomic analyses.
  • Isotopic measurements and geochemical modeling.
  • Biogeographic pattern analysis.

Main Results:

  • Discovery of previously unknown diazotrophic microorganisms.
  • Identification of unusual physiological adaptations in marine microbes.
  • Characterization of nutrient and isotope distributions.
  • Revealed biogeographic patterns of N2 fixation.

Conclusions:

  • Marine nitrogen fixation is more complex and diverse than previously thought.
  • Diazotrophs play a critical role in the global nitrogen cycle.
  • Ocean warming, CO2 increase, and acidification will alter marine N2 fixation dynamics, impacting food webs and biogeochemical cycles.