L18W10_MIC105_NitrogenI

L18W10_MIC105_NitrogenI - * Simplied Nitrogen Cycle Anammox...

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2/19/2010 1 Nitrifcation NH 4 + -> NO 3 - * Nitrogen fxation N 2 -> NH 4 + Denitrifcation NO 3 - -> N 2 Anammox NH 4 + + NO 2 - -> N 2 Simplifed Nitrogen Cycle
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2/19/2010 2 N 2 makes up ~80% of the atmosphere, but usable nitrogen is limiting in many aquatic and soil environments. N= N bond very stable, requires energy to break the bond. The Haber process (N 2 +3 H 2 ->2 NH 3 ) is used to produce 500 million tons of nitrogen fertilizer/year. Requires high temperature, high pressure and a catalyst. Nitrogen Fxation is is widespread among the Bacteria and Archaea and is not associated with any single lineage. No eukaryotes are known to Fx nitrogen. N 2 Fxation *
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2/19/2010 3 Nitrogen fxers * Green sulFur
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2/19/2010 4 Lineages with members capable of nitrogen Fxation: Proteobacteria : some PNS, some PS, Azotobacter , some Desulfovibrio (SRBs), Klebsiella (an enteric) Gram positives , including some clostridia, heliobacteria, certain Bacillus sp., Frankia some cyanobacteria some green sulfur bacteria, some Archaea , including some methanogens. N 2 Fxation *
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2/19/2010 5 Either N 2 fxation was present in an early ancestor and was lost From some lineages, or has been passed by horizontal transFer. Nitrogenase is the key enzyme complex, reduces N 2 to NH 3 . Reaction: N 2 + 8e - + 8H + + ~18 ATP -> 2 NH 3 + H 2 + ~18 ADP + ~20P i 6 electrons are required to reduce N 2 to 2 NH 3 ; but H 2 is always made as a byproduct - so a total oF 8 electrons are utilized. Potential For bioFuel (H 2 ) production N 2 fxation *
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2/19/2010 6 Two protein components. FeS protein (dinitrogenase reductase) transfers electrons from electron donor to the catalytic component: MoFe protein (dinitrogenase). Some organisms produce alternative nitrogenases with different metals: Vanadium (Fe-Va) or Fe-only instead of Fe-Mo. Produced when Mo and/or Va are limiting as a backup mechanism for ±xing N 2 . Azotobacter vinelandii and Rhodopseudomonas palustris (PNS) can produce all three types under various growth conditions. Nitrogenase *
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2/19/2010 7 Nitrogenase reaction * Dinitrogenase (FeMo protein, catalytic compoent) Dinitrogenase reductase (Fe protein, an electron carrier protein) 8e - 8e - 16-24 ATP 2 NH 3 + H 2 N 2 + 8H + Electrons from pyruvate FeMo 4Fe-4S
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2/19/2010 8 Most direct assay to measure N 2 fxation uses the N-15 stable isotope, requires analysis oF the production oF 15-NH 3 by mass spectrometer. Nitrogenase is not specifc For N 2 , and will reduce acetylene to ethylene; used as a characteristic assay For nitrogen fxation using gas chromatography to monitor the reaction. N 2 fxation assays *
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2/19/2010 9 Assay for N 2 Fxation
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2/19/2010 10 N 2 fxation gene cluster ~20 genes are required For nitrogenase production, very homologous in all organisms. Nitrogenase production is highly regulated: only made under
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This note was uploaded on 02/16/2011 for the course MIC 105 taught by Professor Wheelis during the Spring '08 term at UC Davis.

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L18W10_MIC105_NitrogenI - * Simplied Nitrogen Cycle Anammox...

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