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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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Rhizaria are a diverse group of unicellular protists characterized by their threadlike cytoplasmic extensions known as pseudopodia. These structures aid in both locomotion and feeding, giving Rhizaria an amoeboid appearance. Their amoeboid morphology once led to taxonomic confusion, but molecular phylogenetics has clarified their evolutionary placement and emphasized their shared use of pseudopodia despite divergent lineages.This clade comprises diverse lineages such as Chlorarachniophyta,...
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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.
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Organisms exhibit remarkable metabolic diversity, categorized based on how they acquire energy and carbon. These strategies enable survival in various ecological niches and are essential for maintaining energy flow and nutrient cycling within ecosystems.Energy and Carbon SourcesOrganisms are classified as phototrophs or chemotrophs based on energy acquisition. Phototrophs use light as their energy source, while chemotrophs rely on oxidizing chemical compounds. Further differentiation arises...
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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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Related Experiment Video

Updated: Nov 25, 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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Heterotrophic Foraminifera Capable of Inorganic Nitrogen Assimilation.

Clare Bird1,2, Charlotte LeKieffre3,4, Thierry Jauffrais5

  • 1Biological and Environmental Sciences, Faculty of Natural Sciences, University of Stirling, Stirling, United Kingdom.

Frontiers in Microbiology
|December 21, 2020
PubMed
Summary

Heterotrophic protists, like foraminifera, can assimilate inorganic ammonium, a key nutrient in marine ecosystems. This study reveals an innate cellular mechanism for ammonium uptake in these organisms, independent of photosynthesis.

Keywords:
ammonium assimilationforaminiferaheterotrophic protistsheterotrophymarinenitrogen cycle

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Area of Science:

  • Marine microbial ecology
  • Protist biology
  • Biogeochemical cycling

Background:

  • Nitrogen availability is crucial for marine productivity.
  • Ammonium assimilation is vital for marine food webs.
  • Previous studies suggested ammonium assimilation in kleptoplastic foraminifera via imported pathways.

Purpose of the Study:

  • To investigate if heterotrophic protists possess an innate ability for ammonium assimilation.
  • To explore ammonium uptake and assimilation mechanisms in non-photosynthetic foraminifera.
  • To identify new pathways for dissolved inorganic nitrogen assimilation in the marine microbial loop.

Main Methods:

  • Stable isotope labeling with 15N-ammonium and 13C-bicarbonate.
  • Transmission electron microscopy (TEM) for ultrastructural analysis.
  • Quantitative nanoscale secondary ion mass spectrometry (NanoSIMS) imaging for elemental analysis.

Main Results:

  • Two heterotrophic foraminifera species, Ammonia sp. and Globigerina bulloides, did not assimilate 13C-bicarbonate, confirming their lack of photosynthesis.
  • Both species assimilated dissolved 15N-ammonium.
  • Incorporation of 15N-ammonium occurred in organelles crucial for cell growth and development.

Conclusions:

  • Heterotrophic protists possess an innate cellular mechanism for inorganic ammonium assimilation.
  • This finding reveals a previously unrecognized pathway for dissolved inorganic nitrogen assimilation in marine microbes.
  • The study expands our understanding of nitrogen cycling within the marine microbial loop.