Question

What is denitrification?

Answer 1

Denitrification is a microbially aided process that reduces nitrate ($N{O_3}$) to create molecular nitrogen (${N_2}$) via a succession of intermediate gaseous nitrogen oxide products. Denitrification is a type of respiration performed by facultative anaerobic bacteria that decreases oxidised forms of nitrogen in response to the oxidation of an electron donor such as organic materials.

Complete answer:
In order of most to least thermodynamically advantageous, the preferred nitrogen electron acceptors are nitrate ($N{O_3}$), nitrite ($N{O_2}$), nitric oxide ($NO$), nitrous oxide (${N_2}O$), and ultimately dinitrogen (${N_2}$), which completes the nitrogen cycle. Microbes that denitrogenate require a low oxygen content of less than $10\%$ as well as organic C for energy. Denitrification can be strategically utilised to treat sewage or animal leftovers with high nitrogen concentration since it can remove $N{O_3}$ and reduce its leaching to groundwater. Denitrification can cause the release of ${N_2}O$, an ozone-depleting chemical and a greenhouse gas that has a significant impact on global warming.
Heterotrophic bacteria undertake the majority of the work, however autotrophic denitrifiers have also been discovered (e.g., Thiobacillus denitrificans). Denitrifiers are found in all of the major evolutionary groups. In general, numerous bacteria species are involved in the full reduction of nitrate to ${N_2}$, and more than one enzyme pathway has been found. Denitrification not only provides energy to the organism converting nitrate to dinitrogen gas, but some anaerobic ciliates can also employ denitrifying endosymbionts to gain energy, similar to how mitochondria in oxygen-breathing animals are used.

Note:
Denitrification can occur in both terrestrial and marine habitats in nature. Denitrification usually takes place in anoxic conditions, where the amount of dissolved and freely available oxygen is low. Instead of oxygen $\left( {{O_2}} \right),$ a more energetically favourable electron acceptor, nitrate $\left( {NO_3^ - } \right)$ or nitrite $\left( {NO_2^ - } \right)$ can be employed as a substitute terminal electron acceptor in these locations. A terminal electron acceptor is a chemical that receives electrons and is thereby reduced in the process.