This 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. 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.
COGEM released a comprehensive database of pathogenicity assessment of around 2575 bacterial species in 2011. The database ranks the pathogenicity of species on a scale of 1 to 4. Nitrosomonas europaea ranks on this scale: