nitrogen fixation

Examples of nitrogen fixation in the following topics:

• Nitrogenase and Nitrogen Fixation

  • Nitrogen fixation also refers to other biological conversions of nitrogen, such as its conversion to nitrogen dioxide.
  • Nitrogen fixation is a process by which nitrogen (N2) in the atmosphere is converted into ammonia (NH3).
  • Fixation processes free up the nitrogen atoms from their diatomic form (N2) to be used in other ways.
  • Therefore, nitrogen fixation is essential for agriculture and the manufacture of fertilizer.
  • Biological nitrogen fixation (BNF) occurs when atmospheric nitrogen is converted to ammonia by an enzyme called nitrogenase.

• Early Discoveries in Nitrogen Fixation

  • Nitrogen fixation carried out by bacteria helps farmers yield healthy crops.
  • Hermann Hellriegel (1831-1895), a noted German agricultural chemist, discovered that leguminous plants took atmospheric nitrogen and replenished the ammonium in the soil through the process now known as nitrogen fixation.
  • He found that the nodules on the roots of legumes are the location where nitrogen fixation takes place.
  • Hellriegel did not determine what factors in the root nodules carried out nitrogen fixation.
  • These rhizobia perform the chemical processes of nitrogen fixation.

• Symbiosis between Bacteria and Eukaryotes

  • Abiotic nitrogen fixation occurs as a result of lightning or by industrial processes.
  • Biological nitrogen fixation (BNF) is exclusively carried out by prokaryotes: soil bacteria, cyanobacteria, and Frankia spp.
  • Nitrogenase, the enzyme that fixes nitrogen, is inactivated by oxygen, so the nodule provides an oxygen-free area for nitrogen fixation to take place.
  • Through symbiotic nitrogen fixation, the plant benefits from using an endless source of nitrogen: the atmosphere.
  • Explain the need for nitrogen fixation and how it is accomplished

• Nitrogen Fixation: Root and Bacteria Interactions

  • Biological nitrogen fixation (BNF), the conversion of atmospheric nitrogen (N2) into ammonia (NH3), is exclusively carried out by prokaryotes, such as soil bacteria or cyanobacteria.
  • The NH3 resulting from fixation can be transported into plant tissue and incorporated into amino acids, which are then made into plant proteins.
  • Soil bacteria, collectively called rhizobia, symbiotically interact with legume roots to form specialized structures called nodules in which nitrogen fixation takes place .
  • Through symbiotic nitrogen fixation, the plant benefits from using an endless source of nitrogen from the atmosphere.
  • Abiotic nitrogen fixation has been omitted.

• Genetics and Regulation of N2 Fixation

  • Through control of gene expression, nitrogen fixing bacteria can turn on and off the proteins needed for nitrogen fixation.
  • The fixation of atmospheric nitrogen (N2) is a very energy intensive endeavor.
  • The nif genes are genes encoding enzymes involved in the fixation of atmospheric nitrogen.
  • Nitrogen fixation is regulated by nif regulon, which is a set of seven operons which includes 17 nif genes.
  • Discuss the role of the nif genes in controlling nitrogen fixation

• The Nitrogen Cycle

  • Nitrogen is cycled through the earth via the multi-step process of nitrogen fixation, which is carried out by bacteria.
  • Nitrogen enters the living world via free-living and symbiotic bacteria, which incorporate nitrogen into their macromolecules through nitrogen fixation (conversion of N2).
  • Cyanobacteria live in most aquatic ecosystems where sunlight is present; they play a key role in nitrogen fixation.
  • Cyanobacteria are able to use inorganic sources of nitrogen to "fix" nitrogen.
  • The nitrogen that enters living systems by nitrogen fixation is successively converted from organic nitrogen back into nitrogen gas by bacteria .

• The Nitrogen Cycle

  • The nitrogen cycle is the process by which nitrogen is converted from organic to inorganic forms; many steps are performed by microbes.
  • The nitrogen cycle describes the conversion of nitrogen between different chemical forms.
  • Nitrogen is essential for the formation of amino acids and nucleotides.
  • Fixation: In order for organisms to use atmospheric nitrogen (N2), it must be "fixed" or converted into ammonia (NH3).
  • This can happen occasionally through a lightning strike, but the bulk of nitrogen fixation is done by free living or symbiotic bacteria.

• Role of Microbes in Biogeochemical Cycling

  • The key collective metabolic processes of microbes (including nitrogen fixation, carbon fixation, methane metabolism, and sulfur metabolism) effectively control global biogeochemical cycling.
  • The transformative process by which carbon dioxide is taken up from the atmospheric reservoir and "fixed" into organic substances is called carbon fixation.
  • The Earth's atmosphere is primarily composed of nitrogen, but atmospheric nitrogen (N2) is relatively unusable for biological organisms.
  • Consequently, chemical processing of nitrogen (or nitrogen fixation) is necessary to convert gaseous nitrogen into forms that living organisms can use.
  • Almost all of the nitrogen fixation that occurs on the planet is carried out by bacteria that have the enzyme nitrogenase, which combines N2 with hydrogen to produce a useful form of nitrogen (such as ammonia).

• Anaerobiosis and N2 Fixation

  • Nitrogen fixing bacteria have different strategies to reduce oxygen levels, which interfere with nitrogenase function.
  • Central to nitrogen fixation (N2 to NH3) are the enzymes that do the actual fixation, these are known as nitrogenases.
  • Many rhizobia, nitrogen fixing bacteria, live in a symbiotic relationship with plants known as legumes.
  • Leghemoglobin is a nitrogen or oxygen carrier; naturally occurring oxygen and nitrogen interact similarly with this protein.
  • The protein and heme come together to function , allowing the bacteria to fix-nitrogen, giving the plant usable nitrogen and thus the plant provides the rhizobia a home.

• Nitrification

  • Nitrobacter plays an important role in the nitrogen cycle by oxidizing nitrite into nitrate in soil.
  • Nitrification is an important step in the nitrogen cycle in soil.
  • Nitrification is a process of nitrogen compound oxidation (effectively, loss of electrons from the nitrogen atom to the oxygen atoms):
  • As in sulfur and iron oxidation, NADH for carbon dioxide fixation using the Calvin cycle is generated by reverse electron flow, thereby placing a further metabolic burden on an already energy-poor process.
  • Schematic representation of the flow of nitrogen through the environment.