Nitrification is an oxidative biological process that converts ammonia into nitrate. The whole process is composed of two different steps which are performed by different microorganisms: ammonia to nitrite and nitrite to nitrate. The first step is performed by organisms of two domains: Bacteria (genera Nitrosomonas and Nitrosococcus) and Archaea (Crenarchaeota phylum). The second step is driven by Bacteria (gen. Nitrobacter). Nitrification is an important part of the nitrogen cycle.