Nitrosomonas europaea
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Photo: Stan Watson,
Woods Hole Oceanographic Institute
As part of the DOE initiative to explore the role of microorganisms in global carbon sequestration, the Joint Genome Institute is sequencing the autotrophic nitrifying bacterium Nitrosomonas europaea. This organism plays a central role in the availability of nitrogen to plants and hence in limiting C02 fixation. These bacteria are important players in the treatment of industrial and sewage waste in the first step of oxidizing ammonia to nitrate. N. europaea is also capable of degrading a variety of halogenated organic compounds, including trichloroethylene (Arciero et al 1989), benzene (Hyman et al 1985) and vinyl chloride, which may make it an attractive organism for bioremediation.

Nitrosomonas europaea, an Obligate Lithoautotrophic, Ammonia-Oxidizing Bacterium

Nitrosomonas europaea, an autotrophic nitrifying bacterium, is the most studied of the ammonia-oxidizing bacteria that are participants in the biogeochemical N cycle. Nitrifying bacteria play a central role in the availability of nitrogen to plants and hence in limiting CO2 fixation. The reaction catalyzed by these bacteria is the first step in the oxidation of ammonia to nitrate. These bacteria also are important players in the treatment of industrial and sewage waste in the first step of oxidizing ammonia to nitrate. Evidence suggests that ammonia-oxidizing bacteria contribute significantly to the global production of nitrous oxide (produced by the reduction of nitrite). N.europaea also is capable of degrading a variety of halogenated organic compounds, including trichloroethylene, benzene, and vinyl chloride. The ability of nitrifying organisms to degrade some pollutants may make these organisms attractive for controlled bioremediation in nitrifying soils and waters.

Nitrosomonas europaea (UMR)

While not using photosynthesis for energy is not unique, burning ammonia with oxygen is. Both are characteristics of Nitrosomonas europaea. This gram negative chemolithotroph oxidizes ammonia to nitrite and lives in several places such as soil, sewage, freshwater, the walls of buildings and on the surface of monuments especially in polluted areas where air contains high levels of nitrogen compounds. This microbe prefers an optimum pH of 6.0-9.0, fairly neutral conditions, has an aerobic metabolism and prefers a temperature range of 20-30 degrees centigrade. Most are motile with flagella located in the polar regions although some species are nonmotile. A selective medium is needed for isolation. This medium should be completely inorganic and include ammonia as an electron donor, bicarbonate as the sole carbon source, and an extensively washed high purity agar or a silica gel agar. Because of the large amounts of ammonia this bacterium needs to consume for energy to divide, cell division can take up to several days.

Ammonia Chomper

Nitrosomonas europaea is an "ammonia-powered" microbe that uses ammonia as a fuel to live and grow. Power generating membranes (long, thin tubes inside the cell) use electrons from ammonia's nitrogen atom to produce energy. Nitrosomonas europaea can obtain the carbon that it needs to grow by getting it from the atmosphere via "carbon fixation": converting carbon in a gaseous form into carbon bound up in organic molecules. Plants can fix carbon, that is, they can convert carbon dioxide into sugar, using the energy from photosynthesis. This strange bacterium can also fix carbon, but instead of photosynthesis for its energy it uses the energy produced by "burning" ammonia with oxygen. N. europaea must consume large amounts of ammonia before it will divide, and cell division may take up to several days. This microbe, which does not like being exposed to light, will cover itself in slime and form clumps with other microbes to avoid it. Some ammonia-chomping microbes can live in the walls of buildings and on the surfaces of monuments, especially in polluted areas where air contains high levels of nitrogen compounds. When these microbes use ammonia from the air, they produce nitric acid. The acid can dissolve some stone and other construction materials found on statues and in buildings.