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L19W10_MIC105_NitrogenII

L19W10_MIC105_NitrogenII - Nitrogen Cycle Reactions II...

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2/24/2010 1 Nitrification NH 4 + -> NO 3 - * Nitrogen fixation N 2 -> NH 4 + Denitrification NO 3 - -> N 2 Anammox NH 4 + + NO 2 - -> N 2 Assimilatory Nitrate reduction NO 3 - -> NH 4 + Nitrogen Cycle Reactions II
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2/24/2010 2 Nitrification: NH 3 -> NO 2 - -> NO 3 - Anammox: NH 4 + + NO 2 - -> N 2 + 2 H 2 O Denitrification & Nitrate Respiration NO 3 - -> NO 2 - -> NO -> N 2 O -> N 2 l_ > NH 4 + Nitrogen Fixation: N 2 -> NH 3 Nitrogen Assimilation: NH 3 -> organic nitrogen compounds NO 3 - -> NH 3 -> organic nitrogen compounds (assimilatory nitrate reduction) Ammonification: organic nitrogen compounds -> NH 3 Nitrogen Cycle Reactions II *
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2/24/2010 3 Nitrification: oxidation of ammonia to nitrate NH 3 -> NO 2 - -> NO 3 -
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2/24/2010 4 Anion leaching Nitrification * Ammonia oxidizers Nitrite oxidizers NH 4 + -> NO 3 -
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2/24/2010 5 Nitrification: oxidation of ammonia to nitrate Carried out by 2 physiologically distinct groups of organisms Ammonia oxidizers convert ammonia to nitrite NH 3 -> NO 2 - (ex. Nitrosococcus) Nitrite oxidizers convert nitrite to nitrate NO 2 - -> NO 3 - (ex. Nitrobacter ) Both groups are chemolithoautotrophs that use the Calvin cycle to fix CO 2 No organisms are currently known to carry out both steps *
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2/24/2010 6 Nitrifiers *
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2/24/2010 7 Nitrification: oxidation of ammonia to nitrate (NO 3 - ) Ammonia oxidizing bacteria (AOB) are members of the β and γ Proteobacteria NH 3 + 1 1 / 2 O 2 -> NO 2 - + H 2 O Δ G o ’ = -288 kJ/mol *
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2/24/2010 8 Nitrification: oxidation of ammonia to nitrate Ammonia oxidizing bacteria (NH 3 -> NO 2 - ) Key enzymes: 1. A mmonia monooxygenase (AMO) converts ammonia to hydroxylamine (NH 3 -> NH 2 OH) AMO is evolutionarily and functionally related to methane monooxygenase (MMO) which is used by methanotrophs to oxidize methane to methanol (CH 4 -> CH 3 OH) 2. Hydroxylamine oxidoreductase catalyzes NH 2 OH -> NO 2 - *
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2/24/2010 9 Aerobic Ammonia Oxidation Electrons enter the ETC, result in protons pumped and generation of PMF. ATP can be generated as protons enter the cell via a standard ATPase. *
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2/24/2010 10 AOBs: obligate autotrophs? Most ammonia oxidizing bacteria are obligate autotrophs . However, the genome of Nitrosomonas europea revealed the presence of genes for a fructose transporter. The organism was found to grow with fructose or pyruvate as sole carbon sources but only in the absence of CO 2 ... AND it still required ammonium as the energy source and electron donor. An example of chemolithoheterotrophy *
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2/24/2010 11 Ammonia oxidizing bacterium: Nitrosococcus oceani
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2/24/2010 12 Nitrification: oxidation of ammonia to nitrate Nitrite oxidizing bacteria are members of the α , β and δ Proteobacteria and the Nitrospira lineage NO 2 - + H 2 O -> NO 3 - + 2 H + + 2 e - Δ G o ’ = -74 kJ/mol *
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2/24/2010 13 Nitrification: oxidation of ammonia to nitrate Nitrite oxidizing bacteria Key enzyme: Nitrite oxidoreductase catalyzes NO 2 - -> NO 3 - Electrons are used to reduce O 2 through the membrane ETC, protons are pumped, generating PMF and ATP.
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