Nitrification in the Ocean: A Systematic Review

Abstract

Nitrogen forms an essential element for marine organisms and plays a pivotal role in controlling productivity in various parts of the ocean. Nitrogen, being present in various oxidation states ranging from ammonium to nitrate, acts both as an electron acceptor and donor. Nitrification, the oxidation of ammonia to nitrite and nitrate, is probably the dominant type of chemoautotrophic metabolism in the ocean and may be unique in that it takes place in the oxidized water column. Nitrification is a central process in the nitrogen cycle, which is closely associated with phosphorous, carbon and other biologically important components that are essential for the maintenance of the nutrient stoichiometry in the marine environment. The process of nitrification does not influence the net nitrogen stock of the ocean trove except for small alterations in the gaseous pool of nitrous oxide. The group of ammonia-oxidizing bacteria and archaea play an active role in the oxidation of ammonia to nitrite and the group of nitrite oxidizers help in the conversion of nitrite to nitrate, which in turn is taken up by phytoplankton, the producer community of the marine ecosystem, as an essential source of nitrogen. Bacteria are the only groups of ammonia oxidizers and also include anammox species, mediating anaerobic ammonium oxidation with nitrite, present in the marine nitrogen cycle. The autotrophic nitrifying biofilm formed by the nitrifying and the anammox bacteria is found to play a significant role in the process of nitrification.