Nitrosopumilus maritimus is an extremely common archaeon living in seawater. It is the first member of the Group 1a Crenarchaeota to be isolated in pure culture. Gene sequences suggest that the Group 1a Crenarchaeota are ubiquitous with the oligotrophic surface ocean and can be found in most non-coastal marine waters around the planet. It is one of the smallest living organisms at 0.2 micrometers in diameter. It lives by oxidizing ammonia to nitrite. N. maritimus is capable of oxidizing ammonia at levels as low as 10 nanomolar, near the limit to sustain its life. This organism was isolated from sediment in a tropical tank at the Seattle Aquarium by a group led by David Stahl (University of Washington). In taxonomy, "Candidatus Nitrosopumilus" is a genus of the Nitrosopumilaceae.
^http://www.physorg.com/news173538255.html Planet's nitrogen cycle overturned by 'tiny ammonia eater of the seas' Hannah Hickey 2009-09-30 originally based on a Nature publication by Willm Martens-Habbena, David Stahl
^Könneke, Martin; Bernhard, Anne E.; de la Torre, José R.; Walker, Christopher B.; Waterbury, John B.; Stahl, David A. (22 September 2005). "Isolation of an autotrophic ammonia-oxidizing marine archaeon". Nature. 437 (7058): 543–546. doi:10.1038/nature03911. PMID16177789.