Index >> Growth of Microorganism >> Nitrogen Cycle

Nitrogen Cycle -
In nature nitrogen is present in organic form as proteins, and in many inorganic states, the most reduced being NH3^- and the most oxidised. In atmosphere, there is abundant molecular nitrogen.

There are some nitrogen fixing microbes in nature. Fixation of atmospheric nitrogen requires high energy input. Only prokaryotes are capable of biological nitrogen fixation.
The most important group are the rhizobia that form root nodules in leguminous plants. There is some specificity between the bacterial strain and the legume host. Through cross fertilisation the nodulation of specific crops could be increased by inoculation of seeds with appropriate Rhizobjum strains.

Their application could, however, lead to environmental problems. Ammonia is converted first to nitrite and then to nitrate by nitrifying bacteria. Ammonium ions are bound to negatively charged clay particles in soil. However, nitrate ions are readily leached and can reach high concentrations in run off waters and rivers.

This can cause methaemaglobinemia or blue baby disease in animals and infants and can lead to eutrophication. However, it must be clear that none of the nutrient cycles occurs in isolation. For example, decomposition of organic compounds will simultaneously release C, N and other elements and each microbe is involved in cycling of more than one nutrients.