Production of nitric oxide in Nitrosomonas europaea by reduction of nitrite

Nitrosomonas europaea and Nitrosovibrio sp. produced NO and N₂O during nitrification of ammonium. Less then 15% of the produced NO was due to chemical decomposition of nitrite. Production of NO and especially of N₂O increased when the bacteria were incubated under anaerobic conditions at decreasing flow rates of air, or at increasing cell densities. Low concentrations of chlorite (10 M) inhibited the production of NO and N₂, but not of nitrite indicating that NO and N₂O were not produced during the oxidative conversion of ammonium to nitrite. NO and N₂O were produced during reduction of nitrite with hydrazine as electron donor in almost stoichiometric quantities indicating that reduction of nitrite was the main source of NO and N₂O.     

An ammonia-oxidizing bacterium,Nitrosovibrio tenuis nov. gen. nov. sp.

An ammonia-oxidizing, autotroph growing, slender, curved rod was isolated from the soil of Hawaii. It is well distinguishable from any other nitrifying bacteria thus far described by their morphology. The cells are 1.1–3.0 m long and 0.3–0.4 m wide. They are motile by means of 1–4 subpolar to lateral flagella. In contrast to most of the ammonia-oxidizing bacteria the isolated vibrio is void of an extensive cytomembrane system. To categorize this not yet described species we propose to create the new genus Nitrosovibrio and to classify the isolated strain as Nitrosovibrio tenuis.     

Production of nitric oxide by ammonium-oxidizing bacteria colonizing building stones

Abstract Stone samples from corroding historical buildings in Germany released NO in significant amounts during oxidation of ammonium to nitrate. Nitrite intermediately accumulated to low concentrations. Nitrification and NO release were detectable only in stones with neutral pH. Addition of nitrapyrin inhibited both ammonium oxidation and NO production. NO was produced in stone samples containing Nitrosomonas or Nitrosovibrio , but was not produced in samples containing only Nitrobacter . Addition of nitrite stimulated NO production in autoclaved stone samples significantly only if dried to < 2% water content, or in acidic stone samples. In moist neutral stones, NO production was only slightly stimulated by nitrite giving less than about 8% of the NO production observed under nitrifying conditions. Most of the NO production by corroding building stones was apparently due to ammonium-oxidizing nitrifiers.     

Taxonomic diversity of Nitrosovibrio strains isolated from building sandstones

Abstract Five strains of Nitrosovibrio , isolated from building sandstones of historic monuments in Germany, were compared. They were characterized by the presence or absence of carboxysomes, generation time, tolerance to ammonium chloride and sodium chloride, and temperature optima. Three strains were distinguishable by DNA homologies, ultrastructure, and growth mode. Only two strains were closely related, indicated e.g. by a DNA homology of 72%. Taxonomical diversity of the endolithic Nitrosovibrio strains may be related to the existence of microniches in building sandstones. Cell aggregation was observed for endolithic cells and for cells of isolated Nitrosovibrio strains. This could be a response to acidic environments.