Ubiquity and diversity of ammonia-oxidizing archaea in water columns and sediments of the ocean

Nitrification, the microbial oxidation of ammonia to nitrite and nitrate, occurs in a wide variety of environments and plays a central role in the global nitrogen cycle. Catalyzed by the enzyme ammonia monooxygenase, the ability to oxidize ammonia was previously thought to be restricted to a few groups within the beta- and gamma-Proteobacteria. However, recent metagenomic studies have revealed the existence of unique ammonia monooxygenase alpha-subunit (amoA) genes derived from uncultivated, nonextremophilic Crenarchaeota. Here, we report molecular evidence for the widespread presence of ammonia-oxidizing archaea (AOA) in marine water columns and sediments. Using PCR primers designed to specifically target…