Nitrosomonas is a genus of Gram-negative rod-shaped chemoautotrophicbacteria. This organism oxidizes ammonia into nitrite as a metabolic process, known as nitritation. Nitrosomonas are useful in bioremediation. They are important in the nitrogen cycle by increasing the availability of nitrogen to plants while limiting carbon dioxidefixation. The genus is found in soil, freshwater, and on building surfaces, especially in areas that contains high levels of nitrogen compounds. Nitrosomonas prefers an optimum pH of 6.0-9.0 and a temperature range of 20 to 30 °C. Most species are motile with a flagellum located in the polar regions. The organism has power generating membranes, which form long, thin tubes inside the cell. These use electrons from the oxidation of ammonia to produce energy. It obtains the carbon it requires from the atmosphere via carbon fixation, which converts carbon in a gaseous form into carbon bound in organic molecules. Unlike plants, which fix carbon into sugar through energy gained through the process of photosynthesis, Nitrosomonas use energy gained through the oxidation of ammonia to fixgaseous carbon dioxide into organic molecules. Nitrosomonas must consume large amounts of ammonia before cell division can occur, and the process of cell division may take up to several days. This microbe is photophobic, and will generate a biofilm matrix or form clumps with other microbes to avoid light. The species Nitrosomonas europaea has been identified as also being able to degrade a variety of halogenated compounds including trichloroethylene, benzene, and vinyl chloride. Some Nitrosomonas species possess the enzyme urease, which catalyzes the conversion of the urea molecule to two ammonia molecules and one carbon dioxide molecule. Nitrosomonas europaea, as well as populations of soil-dwelling ammonia-oxidizing bacteria, have been shown to assimilate the carbon dioxide released by the reaction to make biomass via the Calvin Cycle, and harvest energy by oxidizing ammonia to nitrite. This feature may explain enhanced growth of AOB in the presence of urea in acidic environments. Some sources regard Nitrobacteraceae to be the family of the genus Nicosomonas.
