Denitrification is a complex microbial process that plays a central role in the nitrogen cycle, facilitating the transformation of nitrates (NO₃⁻) and nitrites (NO₂⁻) into gaseous forms such as nitrogen gas (N₂), nitric oxide (NO), and nitrous oxide (N₂O). This reduction process is carried out predominantly by facultative anaerobic bacteria under oxygen-limited (anoxic) conditions.

The pathway involves multiple enzymatic steps mediated by specialized enzymes, each catalyzing a specific reduction reaction:

Nitrate reductase (Nar or Nap): Reduces nitrate (NO₃⁻) to nitrite (NO₂⁻).
Nitrite reductase (Nir): Converts nitrite to nitric oxide (NO).
Nitric oxide reductase (Nor): Reduces NO to nitrous oxide (N₂O).
Nitrous oxide reductase (Nos): Converts N₂O to dinitrogen gas (N₂), completing the process.