Comammox

Comammox (COMplete AMMonia OXidation) is the name attributed to an organism that can convert ammonia into nitrite and then into nitrate through the process of nitrification. Nitrification has traditionally thought to be a two-step process, where ammonia-oxidizing bacteria and archaea oxidize ammonia to nitrite and then nitrite-oxidizing bacteria convert to nitrate. Complete conversion of ammonia into nitrate by a single microorganism was first predicted in 2006. In 2015 the presence of microorganisms that could carry out both conversion processes was discovered within the genus Nitrospira, and the nitrogen cycle was updated. Within the genus Nitrospira, the major ecosystems comammox are primarily found in natural aquifers and engineered ecosystems.

Complete nitrification step yield more energy (∆G°′ = −349 kJ mol⁻¹ NH₃) than either single oxidation alone (∆G°′ = −275 kJ mol⁻¹ NH₃ for ammonia oxidation to nitrite and ∆G°′ = −74 kJ mol⁻¹ NO₂⁻ for nitrite oxidation to nitrate).