to the discovery of archaea capable of ammonia oxidation, ammonia-oxidizing bacteria (AOB) were considered the only organisms capable of ammonia oxidation. Since their discovery in 2005, two isolates of AOAs have been cultivated: Nitrosopumilus maritimus and Nitrososphaera viennensis. When comparing AOB and AOA, AOA dominate in both soils and marine environments, suggesting that Nitrososphaerota (formerly Thaumarchaeota) may be greater contributors to ammonia oxidation in these environments.