Nitrification is a central process in nitrogen cycling and availability, but also in emissions of the greenhouse gas nitrous oxide, groundwater pollution and eutrophication 7, 8. AOA are ubiquitous and abundant in the environment and play a major role in nitrification, the conversion of ammonia to nitrate via nitrite 6. The discovery of ammonia-oxidising archaea (AOA) 1, 2, 3 represents a major milestone in our understanding of the global nitrogen cycle and biology of archaea 4, 5, 6. Our work synthesises information from a decade of research and provides the first integrative framework to study AOA in a global context. Particularly, we show: (i) the global frequency of AOA is extremely uneven, with few clades dominating AOA diversity in most ecosystems (ii) characterised AOA do not represent most predominant clades in nature, including soils and oceans (iii) the functional role of the most prevalent environmental AOA clade remains unclear and (iv) AOA harbour molecular signatures that possibly reflect phenotypic traits. Here, based on extensive phylogenetic and meta-data analyses of 33,378 curated archaeal amoA sequences, we define a highly resolved taxonomy and uncover global environmental patterns that challenge many earlier generalisations.

AOA have been studied intensively based on the amoA gene (encoding ammonia monooxygenase subunit A), making it the most sequenced functional marker gene. Ammonia-oxidising archaea (AOA) are ubiquitous and abundant in nature and play a major role in nitrogen cycling.

Global distribution of alpha + cities