The document discusses the family Nitrobacteriaceae, which includes bacteria that perform the important process of nitrification. It describes the two stages of nitrification where ammonium is converted to nitrites by Nitrosomonas bacteria and then nitrites are converted to nitrates by Nitrobacter bacteria. There are currently four accepted genera in the family: Nitrobacter, Nitrospina, Nitrococcus, and Nitrosipra. These bacteria are characterized by their ability to use nitrite as their sole energy source and ability to fix carbon through autotrophic pathways.

1. NITROBACTERIACEAE

2. Nitrification
• The conversion of ammonium to nitrate is performed
primarily by soil-living bacteria and other nitrifying bacteria.
In the primary stage of nitrification, the oxidation of
ammonium (NH4+) is performed by bacteria such as the
Nitrosomonas species, which converts ammonia to nitrites
(NO2-). Other bacterial species, such as the Nitrobacter, are
responsible for the oxidation of the nitrites into nitrates
(NO3-).It is important for the nitrites to be converted to
nitrates because accumulated nitrites are toxic to plant life.

4. TYPES OF GENUS
• Nitrobacter
• Nitrospina
• Nitrococcus
• Nitrosipra
• There are currently four genera accepted in the
family. The Nitrobacter is the primary type genus.
The other genera are Nitrospina, Nitrococcus and
Nitrosipra.

5. CHARACTERISTICS
• 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.

6. • They are facultative or obligate lithoautotrophs.
• A lithoautotroph is a microbe which derives energy from reduced
compounds of mineral origin.
• For lithoautotrophic bacteria, only inorganic molecules can be used as
energy sources.
• They fix CO2 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.
• A mixotroph is a microorganism that can use a mix of different sources of
energy and carbon.
• They have all the enzymes of the tricarboxylic acid cycle or krebs cycle.

7. 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 most form coccoid and rod cells.
They may be motile by a flagellum.
• Often the cells have a polar cap of flattened membrane
vescicles. There are regularly arranged particles covering
the inner side of the cytoplasmic and intracytoplasmic
nitrite-oxidising membrane.

8. • 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 proteins.

9. Nitrobacter

10. • Nitrospina: They are slender non-motile rods.
There is only one species N. gracilis. They are
obligate lithoautotrophs. They have glycogen-
like storage inclusion bodies.

11. • 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.

12. • 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.

13. Biochemical tests