Nitrogen Fixing Bacteria Essay

964 words - 4 pages

Nitrogen is essential for all life on this planet, but most of it is in the air, making up about 78% of the earths atmosphere. The growth of all organisms depends on the availability of mineral nutrients, and none is more important than nitrogen, which is required in large amounts as an essential component of proteins, nucleic acids and other cellular constituents. There is an abundant supply of nitrogen in the earth's atmosphere in the form of N2 gas. However, N2 is unavailable for use by most organisms because there is a triple bond between the two nitrogen atoms, making the molecule almost static. In order for nitrogen to be used for growth it must be "fixed" (combined) in the form of ammonium (NH4) or nitrate (NO3) ions. The weathering of rocks releases these ions so slowly that it has a neglible effect on the availability of fixed nitrogen. So, nitrogen is often the limiting factor for growth and biomass production in all environments where there is suitable climate and availability of water to support life.Micro-organisms have a central role in almost all aspects of nitrogen availability and therefore for life support on earth. Some bacteria can convert N2 into ammonia by the process termed nitrogen fixation; these bacteria are either free- living or form symbiotic associations with plants or other organisms (such as termites and protozoa). Other bacteria bring about transformations of ammonia to nitrate, and of nitrate to N2 or other nitrogen gases. Many bacteria and fungi degrade organic matter, releasing fixed nitrogen for reuse by other organisms. All of these processes contribute to the nitrogen cycle.The nitrogen molecules N2 is inert. To break it apart so that its atoms can combine with other atoms requires the input of substantial amounts of energy. Three processes are responsible for most of the nitrogen fixation in the biosphere; atmospheric fixation by lightning, biological fixation and industrial fixation. I will be concentrating on biological fixation or fixation by living organisms. Only prokaryotes, including several species of bacteria, are capable of fixing nitrogen. One of the best- known nitrogen fixing bacteria is Rhizobium. This bacterium lives freely in the soil, and also in the roots of many species of plants, especially legumious plants (belonging to the pea family, such as pees, beans, clover, alfalfa and acacia trees). Rhizobium can only fix nitrogen to a very limited extent when living freely in the soil. Most nitrogen fixation by Rhizobium occurs when it is living in plant roots. The plant and the bacterium coexist in a rather remarkable way, each benefiting from the presence of the other.Rhizobium is found in most soils. When a leguminous plant germinates, its roots produce proteins called lectins which bind to polysaccharides on the cell surface of the bacteria. The bacteria invade the roots, spreading along the root hairs....

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