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Mechanism of nitrogen fixation


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These aerial roots contain a nitrogen-fixing cyanobacterial symbiont.

A research group led by Dr. Yuichi Fujita, associate professor, and Dr. Ryoma Tsujimoto at the Graduate School of Bioagricultural Sciences, Nagoya University, has discovered a transcriptional regulator that controls nitrogen fixation in a cyanobacterium Leptolyngbya boryana. Their paper was published online in on April 21, 2014.

Every plant that we see in this scene depends ultimately on biological nitrogen fixation.

[4] "Crystallographic Structure and Functional Implications of the Nitrogenase Molybdenum-Iron protein from Azotobacter vinelandii", Kim, J. K.; Rees, D. C. Nature, 1992, 360, 553-560.

Nitrogen fixation - University of Edinburgh

Biological fixation of nitrogen is done by specialized organisms like microorganisms like , , and .

[KEYWORDS: Baltic Sea; bloom; cyanobacteria; nitrogen fixation; primary production Phytoplankton photosynthesis; planktonic cyanobacteria; gas vesicles; picoplankton; dynamics; buoyancy]

Prof. Fujita's research group discovered a chromosomal part in the genome that contains many genes related to nitrogen fixationAmong the 50 genes in this part, they selected interesting genes with unknown functions and isolated 11 different mutants, with each lacking the selected genes. Five of these mutants lost nitrogenase activity and could not perform nitrogen fixation. With further investigation, they discovered that one of the undetermined proteins activates transcription of genes for nitrogenase only after it senses that oxygen levels are low enough to allow nitrogenase to operate. If the genes that participate in nitrogen fixation in this cyanobacterium can be implanted in plants, then the plants can grow well without using a chemical fertilizer. Once this protein (named CnfR) operates properly in the plants, they can perform nitrogen fixation only when they need nitrogen and the cellular environment is allowed to drive nitrogenase, which may prevent energy loss caused by excessive nitrogen fixation. The outcome of this research is expected to both enhance food production and address relevant environmental issues in the near future. This PNAS paper was recommended by F1000prime, an online service in which internationally distinguished researchers recommend important articles in medicine and biology.

Cyanobacteria are important in the nitrogen cycle

One natural process that can produce enough heat to fix atmospheric nitrogen is .

The Fe protein and the Mo-Fe protein have been isolated from many of these bacteria, and nitrogen fixation can be shown to occur in cell-free systems in a laboratory when the Fe protein of one species is mixed with the Mo-Fe protein of another bacterium, even if the species are very distantly related.

In the symbiotic nitrogen-fixing organisms such as Rhizobium, the root nodules can contain oxygen-scavenging molecules such as leghaemoglobin, which shows as a pink colour when the active nitrogen-fixing nodules of legume roots are cut open.

Similarly, Azotobacter species can fix nitrogen in the rhizosphere of several plants.
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  • Nitrogen Cycle - Backyard Nature

    There is an abundant supply of nitrogen in the earth's atmosphere - nearly 79% in the form of N2 gas.

  • A simple discussion of the nitrogen cycle in a typical backyard

    Now numerous leguminous plants occur in this desert, with nitrogen-fixing Rhizobium in their root nodules.

  • The Nitrogen Cycle | Earth Science | Visionlearning

    Some of them live independently of other organisms - the so-called free-living nitrogen-fixing bacteria.

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Photosynthesis and nitrogen relationships in leaves of …

The nitrogen fixing activity of free-living, non-photosynthetic, aerobic bacteria is strongly dependent on favorablemoisture conditions, oxygen, and an organic food source. Anaerobic representatives (Clostridium) predominate in grassland andwaterlogged soils and soil aggregates where moisture conditions and organic substrates are available but oxygen supply to themicro-environment of the bacteria is severely restricted.

nitrogen-fixing bacteria | Definition & Types | …

Though about 78% of the Earth's atmosphere is nitrogen, plants and animalsdon't necessarily have an easy time getting all the nitrogen they need. The problem isthat green plants can't use the nitrogen that's free in the atmosphere. Some chemistrymust be done on every molecule of free nitrogen before it becomes useful to most livingthings.

Evolution of Nitrogen Fixation | Science

The process of chemically altering unusable, free atmospheric nitrogeninto a form usable by organisms is referred to as nitrogen fixation. In nature,there are two main ways of "fixing" nitrogen:

Coupling between photosynthesis and nitrogen fixation.

FIRST WAY: Lightning. If you'veever been close to a lightning flash and right afterwards smelled an ammonia-like odor,that was lightning-fixed nitrogen you smelled. Only a relatively small percentage ofnitrogen gets fixed in this way, however. Nature's main nitrogen fixers are...

Nitrogen fixation and photosynthetic oxygen evolution …

Nitrogen-fixing microorganisms, existing abundantly but practicallyinvisibly nearly everywhere, include a few forms of bacteria, the blue-green algae, andsome fungi. Some nitrogen-fixing bacteria live in , or small, bag-likegrowths on the roots of certain plants, especially members of the Bean Family.

Nitrogen fixation and photosynthetic oxygen evolution in ..

Typically, nitrogen-fixing microorganisms do not fix free atmosphericnitrogen to a usable form in one step. Usually one set of organisms converts free nitrogen (N) to ammonia (NH). This ammonia is accompanied by its ammonium ion (NH), which some plants can use. However, mostflowering plants need nitrogen in yet another form, which microorganisms provide byconverting the ammonia to usable nitrate (NO).

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