Nitrification and denitrification are two important steps in the nitrogen cycle . Nitrification, a two step process, leads to the production of NO3-, (Fig. 1). In the first step, ammonia oxidation, NH3 is oxidized to NO2-, and in the second step, nitrite oxidation, NO2- is oxidized to NO3-. Until recently, very little was know about nitrification in high temperature environments. However, in 2008 a thermophilic archaeon, named “Candidatus Nitrosocaldus yellowstonii”, was shown to mediate ammonia oxidation up to 74°C. More recently , NO2- oxidizing bacteria were discovered that are active in temperatures up to 48°C(4). While NH3 oxidation is generally considered to be the rate limiting step, this may not be the case at high temperatures since accumulation of NO2- has been reported in some hot springs where NH3 is the dominant form of inorganic nitrogen (1)
