The bacterial conversion of ammonia to nitrate occurs in two stages: ammonia oxidation and nitrite oxidation. The process is called nitrification and is carried out by two groups of bacteria: ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB).
1. Ammonia oxidation: Ammonia-oxidizing bacteria (AOB) oxidize ammonia (NH3) to nitrite (NO2-) through the enzyme ammonia monooxygenase (AMO). The reaction is as follows:
NH3 + 1.5 O2 → NO2- + 2 H+ + H2O
This reaction is an energy-generating process, and AOB use the energy produced to support their growth and metabolism.
2. Nitrite oxidation: Nitrite-oxidizing bacteria (NOB) oxidize nitrite to nitrate (NO3-) through the enzyme nitrite oxidoreductase (NXR). The reaction is as follows:
NO2- + 0.5 O2 → NO3-
This reaction is also an energy-generating process, and NOB use the energy produced to support their growth and metabolism.
Overall, the bacterial conversion of ammonia to nitrate plays an important role in the nitrogen cycle of the environment, as it converts ammonia, which can be toxic to some organisms, into a less toxic form of nitrogen. Nitrate is also an important source of nitrogen for plants, and it can be further converted to other forms of nitrogen by denitrifying bacteria.