•Members: Nitrosopumilus, Nitrososphaera
•Based on 16S rRNAgene survey, archaea were abundant and widespread in the oceans and soils.
•Their phylogenetic relationship were very close to that of Crenarchaeota, but the genome sequence of Nitrosopumilusmaritimus(a marine nitrifier) suggested that Thaumarchaeotais a distinct phylum of Archaea.
•Nitrosopumilusmaritimusoxidize ammonia to nitrite, the first step in nitrification.