Monday, November 16, 2009

What is the function of bacteria in the nitrogen cycle?

1 )Role of Bacteria in Nitrogen fixation-- Diazotrophs are bacteria that fix atmospheric nitrogen gas into a more usable form such as ammonia





A diazotroph is an organism that is able to grow without external sources of fixed nitrogen.





Examples of organisms that do this are rhizobia and Frankia (in symbiosis) and Azospirillum.





All diazotrophs contain iron-molybdenum nitrogenase systems.





Two of the most studied systems are those of Klebsiella pneumoniae and Azotobacter vinlandii.





These systems are used because of their genetic tractability and their fast growth





In terms of generating nitrogen available to all organisms, the symbiotic associations( Means association with leguminous plant / roots) greatly exceed the free-living species with the exception of cyanobacteria.





2 ) Nitrification and role of nitrfying bacteria -





Nitrification is the biological oxidation of ammonia with oxygen into nitrite followed by the oxidation of these nitrites into nitrates.





Nitrification is an important step in the nitrogen cycle in soil. This process was discovered by the Russian microbiologist, Sergei Winogradsky.





The oxidation of ammonia into nitrite, and the subsequent oxidation to nitrate is performed by two different bacteria (nitrifying bacteria).





The first step is done by bacteria of (amongst others) the genus Nitrosomonas and Nitrosococcus.





The second step (oxidation of nitrite into nitrate) is (mainly) done by bacteria of the genus Nitrobacter, with both steps producing energy to be coupled to ATP synthesis.





All organisms are autotrophs, which means that they take carbon dioxide as their carbon source for growth





Nitrification is a process of nitrogen compound oxidation (effectively, loss of electrons from the nitrogen atom to the oxygen atoms) :





NH3 + O2 → NO2− + 3H+ + 2e−


NO2− + H2O → NO3− + 2H+ + 2e−





3 ) Denitrification and the role of bacteria in it --





Denitrification is the process of reducing nitrate and nitrite, highly oxidised forms of nitrogen available for consumption by many groups of organisms, into gaseous nitrogen, which is far less accessible to life forms but makes up the bulk of our atmosphere.





It can be thought of as the opposite of nitrogen fixation, which converts gaseous nitrogen into a more biologically available form.





The process is performed by heterotrophic bacteria (such as Paracoccus denitrificans, Thiobacillus denitrificans, and various pseudomonads) from all main proteolytic groups. Denitrification and nitrification are parts of the nitrogen cycle.





Denitrification takes place under special conditions in both terrestrial and marine ecosystems.





In general, it occurs when oxygen (which is a more favourable electron acceptor) is depleted, and bacteria turn to nitrate in order to respire organic matter.





Because our atmosphere is rich with oxygen, denitrification only takes place in some soils and groundwater, wetlands, poorly ventilated corners of the ocean, and in seafloor sediments.





Denitrification proceeds through some combination of the following steps:





nitrate → nitrite → nitric oxide → nitrous oxide → dinitrogen gas


Or expressed as a redox reaction:





2NO3- + 10e- + 12H+ → N2 + 6H2O








Denitrification is the second step in the nitrification-denitrification process, the conventional way to remove nitrogen from sewage and municipal wastewater.





It is also an instrumental process in riparian zones for the removal of excess nitrate from groundwater contaminated by fertiliser use.





Direct reduction from nitrate to ammonium (a process known as dissimilatory nitrate reduction to ammonium or DNRA) is also possible for organisms that have the nrf-gene.





This is less common than denitrification in most ecosystems as a means of nitrate reduction.





Reduction under anoxic conditions can also occur through process called anaerobic ammonia oxidation (Anammox), this reaction is expressed as the following:





NH4+ + NO2- → N2 + 2H2O

What is the function of bacteria in the nitrogen cycle?
Its huge. Bacteria convert nitrogen gas, which is unuseable for any other organism, into useable forms like ammonia and nitrate.
Reply:To convert nitrogen into a form that can be used by plants (nitrification)
Reply:I learned this 4 months ago in my science class in 5th grade.





Bacteria change ammonia, and wastes into "fixed" nitrogen which can be used by plants, and other parts are released back into the air. this is important because when an animal dies the corpse doesn't stay there, it rots, this is the effect of those bacteria.
Reply:oh GOD i wish i knew...
Reply:Bacteria play a role in every step of the Nitrogen cycle. besides the basic aid in diagenesis and decomposition of organic matter that will release N 9and other compounds), they are involved in every step of the N cycle.





Bacteria either assimilate the N into cell components or use for an energy source or electron acceptor.





Some of the major pathways mediated by bacteria:


Nitrogen fixation (N2 to NH4)


Nitrification (NH4 to N02 to NO3)


Denitrification (NH4 to NO3 to NO2 to N20 to N2)


Ammonification (NO3 to NO2 to NH4)

daphne

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