Submitted by: Submitted by vaghoja
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Pages: 7
Category: Science and Technology
Date Submitted: 01/28/2016 10:08 PM
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NiTROGEN FIXATION BY rHIZOBIUM
Rhizobium is a genus of gram negative bacteria that lives in the soil and forms an endosymbiotic relationship with the roots of certain legumes by fixing nitrogen from the air into the roots. The bacteria forms colonies in the root nodules where they convert nitrogen from the atmosphere into ammonia which can be used by the plants for metabolism. The plants in turn provide the bacteria with organic compounds which are by products of photosynthesis ad needed by the bacteria for their metabolic activities. In 1888, Beijerinck a Dutchman, isolated and cultivated the first microorganisms from the root of legumes. He called it Bacillus radicicola and is now classified under the genus Rhizobium.
Nitrogen is a macronutrient that is required by all living organisms for the synthesis of proteins, nucleic acids and other nitrogen-containing compounds. The earth’s atmosphere contains about 80% of nitrogen in the form of nitrogen gas (N2). Nitrogen gas cannot be used in this form by most living organisms until it has been reduced which involves bonding with hydrogen to form ammonia. Green plants (autotrophs), use nitrogen to make proteins which then flows through the food chain. Micro-organisms like the decomposers (saprobes) break down the proteins as byproducts of catabolism, releasing ammonium ions. These two processes make up part of the process called the nitrogen cycle. The nitrogen cycle is a series of processes that converts nitrogen gas to organic substances and back to nitrogen in nature. It is a continuous cycle that is maintained by the decomposers and nitrogen fixing bacteria like Rhizobium.
There are three ways in which nitrogen can be fixed. They are
1. Atmospheric fixation-this occurs spontaneously due to lightning; a small amount only is fixed this way.
2. Industrial fixation- the Haber process, which is very energy inefficient, is used to make nitrogen fertilizers....