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Nitrogen cycle. Nitrification is the biological oxidation of ammonia to nitrate via the intermediary nitrite.Nitrification is an important step in the nitrogen cycle in soil.The process of complete nitrification may occur through separate organisms [1] or entirely within one organism, as in comammox bacteria.
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.
In these areas, nitrate (NO 3 −) or nitrite (NO 2 −) can be used as a substitute terminal electron acceptor instead of oxygen (O 2), a more energetically favourable electron acceptor. Terminal electron acceptor is a compound that gets reduced in the reaction by receiving electrons.
The reaction above is the overall half reaction of the process of denitrification. The reaction can be further divided into different half reactions each requiring a specific enzyme. The transformation from nitrate to nitrite is performed by nitrate reductase (Nar) NO 3 − + 2 H + + 2 e − → NO 2 − + H 2 O
Dissimilatory nitrate reduction to ammonium is a two step process, reducing NO 3 − to NO 2 − then NO 2 − to NH 4 +, though the reaction may begin with NO 2 − directly. [1] Each step is mediated by a different enzyme, the first step of dissimilatory nitrate reduction to ammonium is usually mediated by a periplasmic nitrate reductase.
The nitrite ion has the chemical formula NO − 2. Nitrite (mostly sodium nitrite) is widely used throughout chemical and pharmaceutical industries. [1] The nitrite anion is a pervasive intermediate in the nitrogen cycle in nature. The name nitrite also refers to organic compounds having the –ONO group, which are esters of nitrous acid.
In the NO − 3 anion, the oxidation state of the central nitrogen atom is V (+5). This corresponds to the highest possible oxidation number of nitrogen. Nitrate is a potentially powerful oxidizer as evidenced by its explosive behaviour at high temperature when it is detonated in ammonium nitrate (NH 4 NO 3), or black powder, ignited by the shock wave of a primary explosive.
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 ...