Abstract
Aerobic ammonia-oxidizing archaea (AOA) play a crucial role in the global nitrogen cycle by oxidizing ammonia to nitrite, and nitric oxide (NO) is a key intermediate in AOA for sustaining aerobic ammonia oxidation activity. We herein heterologously expressed the NO-forming, copper-containing, dissimilatory nitrite reductase (NirK) from Nitrososphaera viennensis and investigated its enzymatic properties. The recombinant protein catalyzed the reduction of (15)NO(2)(-) to (15)NO, the oxidation of hydroxylamine ((15)NH(2)OH) to (15)NO, and the production of (14-15)N(2)O from (15)NH(2)OH and (14)NO(2)(-). To the best of our knowledge, the present study is the first to document the enzymatic properties of AOA NirK.