sentences:  The second reaction is oxidation of nitrite (NO2−) to nitrate by nitrite-oxidizing bacteria (NOB), represented by the "Nitrobacter" genus.Ammonia oxidation in autotrophic nitrification is a complex process that requires several enzymes, proteins and presence of oxygen.The key enzymes, necessary to obtaining energy during oxidation of ammonia to nitrite are ammonia monooxygenase (AMO) and hydroxylamine oxidoreductase (HAO).