These are Gram-negative, non-sporing non-acid fast rods, which may be pleomorphic or coccoid (Nitrobacter), some are slender rods (Nitrospina), cocci (Nitrococcus) or spiral to comma-shaped (Nitrosipra). They may be motile. They are characterised by their ability to use nitrite as the only energy. They are facultaive or obligate lithoautotrophs. They fix CO2 autotrophically through the Calvin cycle but are not photosynthetic. They grow best in the dark around 28°C at pH between 7.6-7.8 and many grow mixotrophically than lithoautotrophically.They have all the enzymes of the tricarboxylic acid cycle. There are currently four genera accepted in the family. The genus Nitrobacter is the type genus. The other genera are Nitrospina, Nitrococcus and Nitrosipra. The GC content of the DNA is 50-62 mol%.

Genera

Nitrobacter: There are currently three species recognized within this genus, N. winogradskyi, N. hamburgensis and N. vulgaris. They only differ slightly in morphology. They are pleomorphic rods, which may form coccoid cells. They may be motile by a subpolar to lateral flagellum. Often the cells have a polar cap of of flattened membrane vescicles. There are regularly arranged particles covering the inner side of the cytoplasmic and intracytoplasmic nitrite-oxidising membrane. The species are subdivided according to the GC content of the DNA, DNA/DNA homology, serological characteristics and the patterns found of the membrane-bound heme proteins. The GC content of the DNA is 59-62 mol%.

Nitrospina: They are slender non-motile rods. There is onle one species N. gracilis. They are obligate lithoautotrophs. They have glycogen-like storage inclusion bodies.The GC content of the DNA is 58 mol%.

Nitrococcus: The spherical motile cells have one to two flagellae. The marine species N. mobilis is the only species. The inner surface of the tubular membrane system is covered with particles. They are obligate lithoautotrophs. There are present carboxysomes, poly-b-hydroxybutyrate (PHB) and glycogen-like storage materials. The GC content of the DNA is 61 mol%.

Nitrosipra: They are vibrio-like to spiral organisms. There is only one species N. marina . They grow preferentially mixotrophically rather than lithoautotrophically. Particles are arranged in rows on the membranes. There are glycogen-like storage deposits. The GC content of the DNA is 50 mol%.

Species Profiles

N. winogradskyi

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