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Both are soil bacteria
Azobacter and Rhizobiaceae bacterial species are
nitrogen fixers
Azobacter is a free-living bacteria
Rhizobium basically in soil
Most bacteria in soil are about one micron in
length or diameter.
Their size varies with their environment.
Bacteria in -high levels of nutrients ,larger than
those in nutrient- poor .
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The majority of bacteria in soil usually occur as
single cells.
Bacteria sometimes join together in chains or
clusters. They mainly have one of two shapes spheres (called cocci) and rods (called bacilli).
Other bacteria have more varied shapes
including spirals and long thin hyphae (although
these are less common).
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Urea  CO(NH2)2
Ammonia  NH3 (gaseous)
Ammonium  NH4
Nitrate  NO3
Nitrite  NO2
Atmospheric Dinitrogen N2
Organic N
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Plants and bacteria use nitrogen in the form of
NH4+ or NO3It serves as an electron acceptor in anaerobic
environment
Nitrogen is often the most limiting nutrient in
soil and water.
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amino acids
nucleic acids (purine, pyrimidine)
cell wall components of bacteria (NAM).
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These bacteria take nitrogen from the air (which
plants cannot use) and convert it into a form of
nitrogen called ammonium (NH4+), which plants
can use.
The nitrogenase enzyme controls the process,
called nitrogen fixation, and these bacteria are
often called "nitrogen fixers".
It converts atmospheric nitrogen into
ammonium, but in the condition of :
 An easily degradable carbon source is
available
 Any nitrogen compounds such as
ammonium or nitrate, are not already
present in substantial concentrations
 Soil pH levels are between 6 and 9
 High levels of phosphorus are present
 Very low levels of oxygen are present
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These are primarily used to enhance the growth
of several species of plants and crops.
A correct proportion of bacterial growth could
ensure a high quality of biofertilizer
Its capability in maintaining the pH, safe to use
and compatible as chemical fertilizer
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Rhizobium is primarily a gram negative, motile,
non-sporulating rod that requires a plant host.
Species under this genus:
R. phaseoli
R. leguminosarum
R. trifolii
Other genus are cowpeas Rhizobium and
Bradyrhizobium
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Rhizobia belong to a specific group of bacteria that
form a mutually beneficial association, or symbiosis,
with legume plants.
Rhizobia are found in soils of many natural
ecosystems. They may also be present in agricultural
areas where they are associated with both crop
legumes (like soybean) and pasture legumes (like
clover).
Usually, the rhizobia in agricultural areas have been
introduced at sowing by applying an inoculum to the
exterior of the seeds as liquid formations or pellets.
Enteric Gram negative aerobes rods
LACTOSE FERMENTING
(PINK PIGMENT IN MAC
AGAR)
1.
2.
3.
4.
ESCHERICHIA
KLEBSIELLA
ENTEROBACTER
CITROBACTER
NON-LACTOSE
FERMENTING
(NO PINK PIGMENT IN
MAC AGAR)
1. SALMONELLA
2. SHIGELLA
3. PROTEUS
4. MORGANELLA
5. PROVIDENCIA
6. SERRATIA
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Gram negative
Non-sporing
Rods
1-4 X 0.6µm
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Mostly surrounded by flagella (peritrichous) and
are motile
Non-motile enterobacteriaceae are Shigella and
Klebsiella
In Escherichia and Morganella, most of the strain
are motile, but some are non-motile
Special case like Yersinia, contain species that are
motile at 25oC but non-motile at 35 – 37oC
KLEBSIELLA
E.COLI
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Most will grow in wide temperature range in
ordinary culture media including NA and BA
Selective media is required to recover Salmonella
and Shigella
On BA, enterobacteria produce large, shiny, grey
colonies that may be hemolytic
Species that produce hydrogen sulphide often
show a green colour around the subsurface
colonies (Klebsiella) and capsulated strains
(Escherichia) produce large mucoid colonies.
IN NUTRIENT AGAR
IN MACCONKEY AGAR
IN MACCONKEY AGAR
IN BLOOD AGAR
IN SS AGAR
IN XLD AGAR
Exotoxin (enterotoxin) is produced by Shigella
dysenteriae and toxigenic strain of Escherichia
coli (ETEC)
 When lysed, enterobacteria will release
endotoxin from their cell wall
*The feature above is applied to all Gram negative
rods
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There are three antigens possesed by some or all
enterobacteria
O, or somatic antigens, found in the wall of bacterial
cell. These antigen are used to subgroup enterobacteria
such as Salmonella and Escherichia sp. O antigen is
heat-stable.
K, or surface antigen, found surround the cell wall and
can therefore interfere with O antigen grouping. They
can be inactivated, however, by heat. Eg. Vi antigen for
Klebsiella and B antigen for strain of E.coli
H, or flagella antigen, posesses by motile
enterobacteria, they are found in the flagella and are
heat-labile. H antigens are used to identify Salmonella
serovars within their somatic groups
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DISCUSS 5 GENUS OF
ENTEROBACTERIACEAE
INCLUDE –MORPHOLOGY, BIOCHEMICAL
CHARACTERISTIC, IMPORTANCE OF THE
CULTURE.