Microbiology Procedure

Index >> Growth of Microorganism >> Nitrogen Cycle

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Growth of Microorganism Growth of Microorganisms Part 2 Lag phase Exponential phase Deceleration Phase Acceleration Phase Stationary Phase Death Phase Mycelial Growth Synchronous Growth Fed Batch Culture Continous Culture Distribution of Microorganisms Environmental Factors affecting Microbial Growth Biogeochemical Cycling of Elements

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.
Other associations are also of agricultural value, particularly root nodules in nonlegumes by actinomycetes (Frankia) and biological nitrogen fixation by cyanobacteria in paddy fields. Nitrogen fixation is a rate limiting step of the nitrogen cycle, summarized. There should be an efficient cycling between organic and inorganic forms of nitrogen.
Inorganic nitrogen in the form of NH3 or NO) is converted to organic form mainly by the plants and microorganisms. NO) nitrate is reduced first to NH3. Microbes differ in their ability to use an inorganic source of nitrogen. The organic nitrogenous compounds are converted to ammonia mainly by the microorganisms. For this mineralisation of organic nitrogen, the microbes degrade dead organic matter and the animal excretory products. In traditional farming systems, mineralisation has provided enough NH3 for plants.
However, this could hardly satisfy the nitrogen requirements of modern, intensive agriculture. This led to dramatic increase in the chemical fixation of nitrogen by the Haber process. Approximately 25% of all fixations are now carried out industrially for the production of ammonium based fertilisers.
	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.

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Growth of Microorganisms Part 2 Carbon Cycle Nitrogen Cycle Sulphur Cycle Chemical Composition of E.Coli Cell Carbon Requirement of Microorganisms Nitrogen & Sulphur Requirement of Microorganisms Microorganisms Classification Based on Oxygen Requirement Microorganisms Nutritional Classificatione Carbon & Energy Source Microorganisms Classification

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