LAUSR

Ammonia-oxidizing Archaea, or Thaumarchaeota (Spang et al., 2010), are an abundant and widespread group of prokaryotes. They are particularly abundant in the mesopelagic zone of the open ocean (Karner et al., 2001) and in oxygen minimum zones (OMZs: Ulloa et al., 2012; Tolar et al., 2013; Peng et al., 2016), where they persist at oxygen concentrations that are at the limit of analytical detection. They perform an important geochemical process: the oxidation of ammonia to nitrite using molecular oxygen as an electron acceptor, the first step in the two-step process of nitrification. They also produce nitrous oxide, an ozone-destroying greenhouse gas, as a byproduct of their metabolism (Santoro et al., 2010; Santoro et al., 2011; Peng et al., 2016). They have proven difficult to isolate into pure culture and most of our knowledge of their ecophysiology stems from experiments with environmental samples or from work with the original isolate, Nitrosopumilus maritimus strain SCM1.