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The Nitrogen cycle is basically a nutrient cycle that describes that how nitrogen is made and stored.
The nitrogen compounds that bacteria can make are called Nitrates.
The nitrates are taken by plants through their roots. Where as other bacteria in the soil take in the nitrates and release nitrogen back into the air.
The conversion of atmospheric nitrogen into inorganic or organic usable forms through the agency of living organism is called biological nitrogen fixation. Soil contains a number of free living nitrogen fixing organisms. These include a number of aerobic and anaerobic bacteria and blue green algae.
Biological nitrogen fixation occurs when atmospheric nitrogen is converted to ammonia by an enzyme called nitrogenase. The process is coupled to the hydrolysis of 16 equivalents of ATP and is accompanied by the co-formation of one molecule of H2. In free-living diazotrophs, the nitrogenase-generated ammonium is assimilated into glutamate through the glutamine synthetase/glutamate synthase pathway.
Enzymes responsible for nitrogenase action are very susceptible to destruction by oxygen. (In fact, many bacteria cease production of the enzyme in the presence of oxygen). Many nitrogen-fixing organisms exist only in anaerobic conditions, respiring to draw down oxygen levels, or binding the oxygen with a protein such as Leghemoglobin.
Plants that contribute to nitrogen fixation include the legume family –Fabaceae. They contain symbiotic bacteria called Rhizobia within nodules in their root system, producing nitrogen compounds that help the plant to grow and compete with other plants. When the plant dies, the fixed nitrogen is released; making it available to other plants and this helps to fertilize the soil.
Certain bacteria can use nitrogen from the air to make nitrogen-containing substances called nitrites.
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