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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 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.
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 ...
The conversion of nitrite to nitrate is facilitated by nitrite-oxidizing bacteria. The genus Nitrobacter is widely distributed in both aquatic and terrestrial environments. [ 2 ] Nitrifying bacteria have an optimum growth between 77 and 86 °F (25 and 30 °C), and cannot survive past the upper limit of 120 °F (49 °C) or the lower limit of 32 ...
Comammox (COMplete AMMonia OXidation) is the name attributed to an organism that can convert ammonia into nitrite and then into nitrate through the process of nitrification. [1] Nitrification has traditionally been thought to be a two-step process, where ammonia-oxidizing bacteria and archaea oxidize ammonia to nitrite and then nitrite ...
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.
Step 1 details the oxidation of ammonia into nitrite via ammonia-oxidizing bacteria. The most frequent genus of bacteria identified as being the facilitator of this step is Nitrosomonas . [ 12 ] These bacteria will produce small quantities of nitrous oxide from produced nitrite in a side reaction. [ 13 ]