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The second reaction is oxidation of nitrite (NO − 2) to nitrate by nitrite-oxidizing bacteria (NOB), represented by the members of Nitrospinota, Nitrospirota, Pseudomonadota, and Chloroflexota. [5] [6] This two-step process was described already in 1890 by the Ukrainian microbiologist Sergei Winogradsky.
Nitrite oxidoreductase (NOR or NXR) is an enzyme involved in nitrification.It is the last step in the process of aerobic ammonia oxidation, which is carried out by two groups of nitrifying bacteria: ammonia oxidizers such as Nitrosospira, Nitrosomonas, and Nitrosococcus convert ammonia to nitrite, while nitrite oxidizers such as Nitrobacter and Nitrospira oxidize nitrite to nitrate.
The process of nitrification begins with the first stage of ammonia oxidation, where ammonia (NH 3) or ammonium (NH 4 +) get converted into nitrite (NO 2-). This first stage is sometimes known as nitritation. It is performed by two groups of organisms, ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA [2]).
The first step is the partial nitrification (nitritation) of half of the ammonium to nitrite by ammonia oxidizing bacteria: 2 NH + 4 + 3 O 2 → 2 NO − 2 + 4 H + + 2 H 2 O. The remaining half of the ammonium and the newly formed nitrite are converted in the anammox process to diatomic nitrogen gas and ~15 % nitrate (not shown) by anammox ...
In the oceans, nitrite-oxidizing bacteria such as Nitrobacter are usually found in close proximity to ammonia-oxidizing bacteria. [11] These two reactions together make up the process of nitrification. The nitrite-oxidation reaction generally proceeds more quickly in ocean waters, and therefore is not a rate-limiting step in nitrification.
Nitrobacter winogradskyi is a gram-negative nitrite-oxidizing bacteria from the genus of Nitrobacter. [2] [3] It is a chemolithoautotroph that derives energy by oxidation of nitrite. Nitrobacter winogradskyi is rod-shaped and is involved in the biological nitrification process that occurs within the nitrogen cycle.
Oxygen is required in both ammonia and nitrite oxidation, meaning that both nitrosifying and nitrite-oxidizing bacteria are aerobes. As in sulfur and iron oxidation, NADH for carbon dioxide fixation using the Calvin cycle is generated by reverse electron flow, thereby placing a further metabolic burden on an already energy-poor process.
Bacteria in the Planctomycetota that are anammox ... Labeled diagram of an anammox cell. ... Anammox is the process of oxidizing ammonium where nitrite acts as the ...