This is an archeael family that contains ammonia monooxygenase subunit A. Ammonia monooxygenase is an enzyme that oxidises ammonia to nitrite and nitrate, thus playing a significant role in the nitrogen cycle. Ammonia-oxidising archaea (AOA) are widespread in marine environments [1].

1: Ubiquity and diversity of ammonia-oxidizing archaea in water columns and sediments of the ocean. Francis CA, Roberts KJ, Beman JM, Santoro AE, Oakley BB; Proc Natl Acad Sci U S A. 2005;102:14683-14688. PMID:16186488