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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.
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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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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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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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Genomics, transcriptomics, and laboratory experiments link bioconvection to nitrogen fixation.

Francesco Di Nezio1,2, Juan Diaz-Miyar1, Antoine Buetti-Dinh1

  • 1Anoxic Aquatic Systems Group, Institute of Microbiology, Department of Environment, Constructions and Design, University of Applied Sciences and Arts of Southern Switzerland (SUPSI), Mendrisio, Switzerland.

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Summary

Anoxygenic phototrophic sulfur bacteria in Lake Cadagno actively fix nitrogen, with nitrogen fixation genes upregulated and linked to bioconvection. This study reveals their crucial role in anoxic ecosystems and biogeochemical cycling.

Keywords:
euxinic bottom zonegenomesmeromictic Lake Cadagnomodern analogsnitrogen fixationphototrophic sulfur bacteria

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Area of Science:

  • Microbiology
  • Environmental Science
  • Biogeochemistry

Background:

  • Lake Cadagno hosts diverse anoxygenic phototrophic sulfur bacteria in its stable euxinic chemocline.
  • These bacteria are vital for understanding early photosynthesis but are poorly characterized due to rare anoxic environments.

Purpose of the Study:

  • To characterize the genetic and ecophysiological traits of anoxygenic phototrophic sulfur bacteria in Lake Cadagno.
  • To investigate the potential for nitrogen fixation in these bacteria and its ecological implications.

Main Methods:

  • Generated high-quality genomes for two purple sulfur bacteria (PSB) and two green sulfur bacteria (GSB).
  • Analyzed chemocline transcriptomes and performed comparative genomic analyses of nitrogen fixation (nif) genes.
  • Conducted laboratory growth experiments under nitrogen-limited conditions.

Main Results:

  • Nitrogen fixation (nif) genes were upregulated in the chemocline, linked to bioconvection.
  • PSBs showed higher abundance and diversity of nif genes than GSBs.
  • PSBs and one GSB species demonstrated the ability to grow using atmospheric nitrogen.

Conclusions:

  • Genomic, transcriptomic, and experimental data confirm active nitrogen fixation in dominant phototrophic sulfur bacteria.
  • A functional coupling between nitrogen cycling and physical mixing processes (bioconvection) is suggested.
  • Findings offer new insights into the ecological roles of anoxygenic phototrophs in stratified anoxic systems.