The Nitrogen Cycle
Under normal circumstances, nitrogenous pollutants like ammonia and nitrates are naturally bioremediated by nitrifying and denitrifying bacteria: ammonia (NH3) is aerobically converted to nitrate (NO3-), and nitrate is anaerobically converted to nitrogen gas (N2).
Nitrosomonas bacteria oxidize ammonia to nitrite: NH3 → NO2-
Nitrosomonas
Nitrobacter then oxidize nitrite to nitrate: NO2- → NO3-
Nitrobacter
Denitrifying bacteria anaerobically reduce nitrate to nitrogen gas: NO3- → N2
Pseudomonas aeruginosa - a denitrifier
This process balances the influx of fixed nitrogen with the outflow of nitrogen gas to the atmosphere. However, due to anthopogenic nitrogen input (fertilizer and waste), fixed nitrogen is often added to soil and groundwater faster than it can be converted to N2, thus leading to nitrogen contamination. Therefore, many strategies for bioremediating nitrogenous compounds is to enhance the capabilities of the nitrifying and denitrifying bacteria.
Nitroaromatic degradation
While ammonia and nitrate are the main nitrogenous pollutants of concern, bacteria can assist in the degradation of nitroaromatics as shown in the reaction pathway for nitro-benzene metabolism below.
Sources:
Spiro (2003); Kunert (2004); Nishino (1993)