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Nodules 25 nodule formaaon step 1 recogniaon and

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Unformatted text preview: S) –  nitrogen fixaAon. 19 Brock Biology of Microorganisms, 13th EdiAon. Nitrogen fixaAon •  Only certain prokaryotes can fix nitrogen (N2); a lot of energy is required because of the triple bond (N≡N). •  Nitrogen fixaAon is one of the most important microbial processes on earth. In the absence of ferAlizers, other organisms are dependent on nitrogen fixers. •  Some nitrogen fixers are free- living (ex.: Cyanobacteria) and others are symbioAc (ex.: Rhizobium). 20 Brock Biology of Microorganisms, 13th EdiAon. Nitrogen fixaAon •  ReacAon is catalyzed by nitrogenase complex (metal cofactors) •  8 electrons are required, 2 are lost as H2 in the process. •  •  Ammonia is the final product and is used to produce amino acids, etc. Dinitrogenase reductase is inhibited by the presence of oxygen. 21 Brock Biology of Microorganisms, 13th EdiAon. Free- living Nitrogen fixers •  Azotobacter, Beijerinckia and Clostridium. •  Widespread in soil, require a soil rich in organic maber to provide energy for nitrogen fixaAon. •  Produce ammonia that can be used by plants (NH3, dissolves in water to produce ammonium NH4). •  Clostridium: strict anaerobe. •  Azotobacter: strict aerobe. The enzyme is protected by a very high rate of O2 consumpAon, which keeps the intracellular e...
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