       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 .

   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 these are less common).

(although

       Urea  CO(NH 2 ) 2 Ammonia  NH 3 (gaseous) Ammonium  NH 4 Nitrate  NO 3 Nitrite  NO 2 Atmospheric Dinitrogen  N 2 Organic N

   Plants and bacteria use nitrogen in the form of NH 4 + or NO 3 It serves as an electron acceptor in anaerobic environment Nitrogen is often the most limiting nutrient in soil and water.

   amino acids nucleic acids (purine, pyrimidine) cell wall components of bacteria (NAM).

  These bacteria take nitrogen from the air (which plants cannot use) and convert it into a form of nitrogen called ammonium (NH 4 + ) , 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

   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

 

1.

2.

3.

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

   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. ESCHERICHIA 2. KLEBSIELLA 3. ENTEROBACTER 4. CITROBACTER

NON-LACTOSE FERMENTING (NO PINK PIGMENT IN MAC AGAR)

1. SALMONELLA 2. SHIGELLA 3. PROTEUS 4. MORGANELLA 5. PROVIDENCIA 6. SERRATIA

    Gram negative Non-sporing Rods 1-4 X 0.6µm

    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 25 o C but non-motile at 35 – 37 o C

KLEBSIELLA E.COLI

    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

coli (ETEC) and toxigenic strain of Escherichia  When lysed , enterobacteria will release endotoxin from their cell wall *The feature above is applied to all Gram negative rods

 1.

2.

3.

There are three antigens possesed by some or all enterobacteria O, or somatic antigens heat-stable.

, found in the wall of bacterial cell. These antigen are used to subgroup enterobacteria such as Salmonella and Escherichia sp. O antigen is 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

  DISCUSS 5 GENUS OF ENTEROBACTERIACEAE INCLUDE –MORPHOLOGY, BIOCHEMICAL CHARACTERISTIC, IMPORTANCE OF THE CULTURE.