Denitrification

This respiratory process [|reduces] oxidized forms of nitrogen in response to the oxidation of an [|electron donor] such as [|organic matter]. The preferred nitrogen [|electron acceptors] in order of most to least thermodynamically favorable include [|nitrate] (NO3−), [|nitrite] (NO2−), [|nitric oxide] (NO), and [|nitrous oxide] (N2O)and dinitrigen [N2]. In terms of the general [|nitrogen cycle], denitrification completes the cycle by returning N2 (dioxide) to the atmosphere. The process is performed primarily by [|heterotrophic] [|bacteria] (such as // [|Paracoccus denitrificans] // and various [|pseudomonads] ), [|[1]] although autotrophic denitrifiers have also been identified (e.g., // [|Thiobacillus] denitrificans//). [|[2]] Denitrifiers are represented in all main phylogenetic groups. [|[3]] Generally several species of bacteria are involved in the complete reduction of nitrate to molecular nitrogen, and more than one enzymatic pathway have been identified in the reduction process. Direct reduction from nitrate to [|ammonium], a process known as dissimilatory nitrate reduction to ammonium or DNRA, [|[5]] is also possible for organisms that have the nrf- [|gene]. [|[6]] This is less common than denitrification in most ecosystems as a means of nitrate reduction. Other genes known in microorganisms which denitrify include //nir// (nitrite reductase) and //nos// (nitrous oxide reductase) among others; [|[7]] organisms identified as having these genes include// [|Alcaligenes faecalis] //, //Alcaligenes xylosoxidans//, many in the //Pseudomonas// genus, // [|Bradyrhizobium japonicum] //, and //Blastobacter denitrificans.//
 * Denitrification** is a microbially facilitated process of nitrate reduction that may ultimately produce molecular [|nitrogen] (N2) through a series of intermediate gaseous nitrogen oxide products.