Nitrogen Cycle

From MicrobeWiki, the student-edited microbiology resource

Nitrogen cycle & Greenhouse Gases

The nitrogen cycle is an important chemical cycle which occurs in the ecosystem. The nitrogen cycle begins when atmospheric N2 is transformed by organisms to NH4. This NH4 is than converted into nitrite which is later converted into nitrate, and the process further repeats itself. The nitrogen cycle is important because it results in important compounds being produced which are essential for proper growth of plants and other organisms.

Nitrogen cycle processes

Nitrogen fixation Nitrogen Mineralization Nitrification occurs in aerobic conditions Denitrification- occurs in anaerobic conditions

Nitrogen fixation

Atmospheric nitrogen (N2) is abundant, but unavailable for biological activity due to the high energy required to break the triple bond. In nitrogen fixation, atmospheric nitrogen is reduced to biologically useful ammonia (NH3) by the activity of prokaryotes utilizing a nitrogenase.


The reaction catalyzed by nitrogenase is N2 + 8H+ + 8e- ---> 2NH3 + H2. Ammonia produced in this way is rapidly protonated to NH4+. Nitrogenases are irreversibly inhibited by exposure to O2, and thus organisms must take steps to prevent this. Some organisms, such as azotobacter protect their nitrogenases with a thick capsule that slows oxygen diffusion. Others, such as the cyanobacteria nostoc form special cells with thick cell walls to exclude oxygen, allowing the cell to provide fixed nitrogen to its neighbors. Alternative nitrogenases do exist that are not deactivated by oxygen, but they are found in a relatively small number of organisms.


Nitrogen fixed by prokaryotes constitutes the vast majority of all biologically active nitrogen on the planet. Nitrogen-fixers may be aerobic or anaerobic, and may be free-living or in a symbiotic relationship with a plant.

Nitrogen Mineralization

Subsection 2a

Subsection 2b

Atmospheric N2 into NH4+


Subsection 3a

Subsection 3b

NH4+ to NO3-


Subsection 4a

Subsection 4b

NO3- to Atmospheric N2, happens in anaerobic conditions

Key Microorganisms in Nitrogen cycle

Bacteria involved- nitraosomas, nitrobacter, e.g. Nitrobacter hamburgensis, Nitrobacter winogradskyi,are key players in the nitrogen cycle

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Greenhouse gases

Topic of your choice.

Current Research

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The Center of Limnology is currently studying the rise in organic nitrogen availability to microbes. Their findings may lead to an analysis of the consequences of anthropogenic nitrogen enrichment watersheds. To learn more visit their website at


[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

Edited by student of Kate Scow