The New Developments Made in the Autotrophic and Heterotrophic Ammonia Oxidation

Abstract

Nitrification is defined as conversion of the ammonium(NH4+-N) to nitrate and it is generally divided into two categories: autotrophic nitrification and heterotrophic nitrification. With the metagenomes retrieved from the Nitrospira highly enriched biosamples, both the ammonium oxidation gens (full set of AMO and hydroxylamine dehydrogenase (HAO) genes) and nitrite oxidoreductase (NXR) coding genes necessary for nitrite oxidation were found in a completely nitrifying bacterium from the genus Nitrospira. Various species of Nitrospira (containing phylogenetically distinct ammonia monooxygenase and hydroxylamine dehydrogenase genes) had been found in many engineered systems and were proved to be comammox bacterium. Some anammox bacteria were found to use mono or dimethylamine and even methanol as electron donors, but the enzymes the employed in the special metabolism were not known. Many heterotrophic nitrifying bacteria have been isolated and characterized from soil, activated sludge, wastewater treatment system. A denitrification process was developed with poly(3-hydroxybutyrate) (PHB) granulesas source of carbon for denitrification. It is possible from metabolic foundations that the heterotrophic nitrifier can consume intracellular stored PHB as the alternative carbon source. This direction still waiting for further exploration.