4.5 AZOBACTER AND RHIZOBIUM
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Transcript of 4.5 AZOBACTER AND RHIZOBIUM
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4.5 AZOBACTER AND RHIZOBIUM
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Introduction 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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Azobacter
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Azobacter - Soil bacteria 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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Forms of Nitrogen Urea CO(NH2)2 Ammonia NH3 (gaseous) Ammonium NH4 Nitrate NO3 Nitrite NO2 Atmospheric Dinitrogen N2 Organic N
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Roles of Nitrogen Plants and bacteria use nitrogen in the
form of NH4+ or NO3
-
It serves as an electron acceptor in anaerobic environment
Nitrogen is often the most limiting nutrient in soil and water.
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Nitrogen is a key element for
amino acids nucleic acids (purine, pyrimidine) cell wall components of bacteria (NAM).
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As nitrogen fixer 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".
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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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Benefits as biofertilizer 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 Rhizobium is primarily a gram negative,
motile, non-sporulating rod that requires a plant host.
Species under this genus:1. R. phaseoli2. R. leguminosarum3. R. trifolii
Other genus are cowpeas Rhizobium and Bradyrhizobium
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In agricultural 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.
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Rhizobium
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4.6 ENTEROBACTERIACEA
EEnteric Gram negative
aerobes rods
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Sub-grouping LACTOSE FERMENTING(PINK PIGMENT IN MAC AGAR)
NON-LACTOSE FERMENTING(NO PINK PIGMENT IN MAC AGAR)
1. ESCHERICHIA2. KLEBSIELLA3. ENTEROBACTER4. CITROBACTER
1. SALMONELLA2. SHIGELLA3. PROTEUS4. MORGANELLA5. PROVIDENCIA6. SERRATIA
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Morphology Gram negative Non-sporing Rods 1-4 X 0.6µm
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Motility 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
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KLEBSIELLA E.COLI
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Culture 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.
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E.coliIN NUTRIENT AGAR IN MACCONKEY AGAR
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Klebsiella spIN MACCONKEY AGAR IN BLOOD AGAR
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Salmonella spIN SS AGAR IN XLD AGAR
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Toxin production 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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Serology There are three antigens possesed by some or all
enterobacteria 1. 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.
2. 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
3. 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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Antigenic structure of Enterobacteriacea
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TASKS DISCUSS 5 GENUS OF
ENTEROBACTERIACEAE INCLUDE –MORPHOLOGY,
BIOCHEMICAL CHARACTERISTIC, IMPORTANCE OF THE CULTURE.
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The end