Friday, January 20, 2012

Bacteria



General characters of bacteria
1. They are prokaryotic, unicellular organism.
2. They have incipient nucleus.
3. Cell organelles such as mitochondria, golgi apparatus, plastids, endoplasmic reticulum
etc are absent.
4. They possess circular DNA.
5. Cell wall is made of by peptidoglycan.
6. Ribosome are 70S types.
7. Photosynthetic pigments are bacteriochlorophyll and chlorobium chlorophyll.
8. Reserve food materials are glycogen and lipids.
9. Common mode of reproduction is binary fission.
10. Sexual reproduction is absent.
Structure
The size of bacteria cell is 0.15um- 500um. According to the shape and arrangement bacteria
are divided into 3 major forms.





a. Cocci (Coccus): These are spherical or globular bacteria. They lack flagella. They show
following types:
i. Monococcus in single cell.
ii. Diplococcus are found in the pairs.
iii. Tetracoccus are found in tetra.
iv. Streptococcus is found in the chain.
v. Staphylococcus is found in irregular group.
b. Bacillus: They are cylindrical, rod- shaped bacteria. Bacillus are divided into following types:
i. Monobacillus found in one rod like structure.
ii. Diplobacillus found in pair joining end to end of two cells.
iii. Streptobacillus found in a chain.
iv. Palisade found in parallel.
c. Spirilla they possess spirally coiled body.
i. Spirilla : they are long and coiled spirally many times.
ii. Vibrios: they show a single curve, like comma shape.
On the basis of number of flagella, the bacteria cell can be divided into following types
i. Atrichous: flagella absent.
ii. Monotrichous: having single flagella.
iii. Polytrichous: many flagella on the cell.
iv. Cephalotrichous: group of flagella arise at one end of cell.
v. Lophotrichous: groupe of flagella arise at both pole of the cell.
Cell structure of bacteria
A bacterial cell is surrounded by a cell wall and plasma membrane. Many bacteria cell have
additional layer is slime layer or capsule. In motile bacteria, flagella are present. Cytoplasm
consists of gas vacuoles, reserve food materials, 70S ribosome, mesosome, plasmids, circular
DNA etc.



Cell wall: it is the outer rigid covering of the cell. Cell wall provides shape to the cell and
protection to the protoplast.
Slime layer: it is surrounded the cell wall. It is made of mucilage. It protects the bacteria cell
against chemical.
Cytoplasm and cell organelles: cytoplasm is the fluid part of cell. It content 70S ribosome,
reserve food material, mesosome, circular DNA, photosynthetic pigment etc.
Mesosome: They are the inner folding finger like structure formed by the plasma membrane in
many bacteria.
Function of mesosome:
i)It is the site for catabolic anabolic pathway.
ii) It helps in cell division and reproduction.
Plasmid: Bacteria have extra chromosome is called plasmid. Plasmids carry some important
genes like nitrogen fixing gene, fertility gene etc.
Flagella: flagella are long thread like structure. It helps in locomotion and movement of bacteria.
Pilli: it is a minute hair like structure. It helps in attachment of bacteria during conjugation.
Gram’s strain in bacteria
Grams 1884 developed a technique of straining of bacterial cell known as Gram’s staining. On
the basic of staining bacteria divided into
a. Gram positive bacteria
i)Cell wall is 25-30nm thick
ii)They show the effect (susceptible) to antibiotics.
iii)Lipopolysaccharide layer is absent
iv) They retain gram’s strin

Eg: Staphylococcus, Streptococcus
b. Gram negative bacteria.
i) Cell wall is 10-15 nm thick
ii)They are more resistant to antibiotic.
iii)Lipopolysaccharide layer is present
iv)They do not retain gram’s stain

 Eg: Rhizobium, Vibrio, Salmonella

Mode of nutrition of bacteria
Bacteria show the both autotrophic and heterotrophic mode of nutrition.
Autotrophic bacteria
They synthesis their own food from inorganic substances. They are two types
i. Photoautotrophic bacteria: they use solar energy for synthesizing their organic
foods. Eg: Chlorobium.
12H2S+ 6CO2----light----------> C6H12O6+6H2O+12S
ii. Chemoautotrophic bacteria: synthesis of their food from oxidation of simple
inorganic compounds. Eg: Hydrogenomonas.
H2+1/2O2 ---------------->H2O + energy
Heterotrophic bacteria
These bacteria can’t synthesize their own food. They obtain their food from other organisms.
These are following types
i. Saprophytic bacteria: they are free bacteria and food obtains from dead and decay
organic substance. Eg: Pseudomonas
ii. Symbiotic bacteria: these bacteria live in mutual beneficial association with other
organisms and share the benefits. Eg: Rhizobium lives in roots nodule of legumes,
from which it obtains food and shelter. In return, it helps plants by fixing nitrogen.
iii. Parasitic bacteria: they live in other organisms for obtaining organic compounds for
their growth. Eg: Salmonella typhi
Economic importance of bacteria
Beneficial effect of bacteria
i. Role in agriculture
a. Natural’s scavenger: saprophytic bacteria cause decay and decompose of dead
organisms and release the raw materials for new generation.
b. Nitrogen fixation: some bacteria fixed the atmospheric nitrogen into ionic
nitrogen. It is utilized in plant.
c. Manure: saprophytic bacteria convert farm refuse, dung and other organic waste
into manure.
d. Gobar gas plant: bacteria convert animal dung and other organic waste into
manure along with production fuel gas.
e. Sewage disposal: organic content of sewage is broken down by bacteria.
ii. Role in industry
a. Dairy industry: milk converted into curd, cheese etc with the help of bacteria.
b. Manufacture of organic compound: bacteria produce the several compound i.e.
butyl alcohol, acetone etc
c. Fibre retting: stem and leaf fibre of plants is separated from other softer tissue by
the action of bacteria.
d. Production of antibiotics: numbers of antibiotics are obtained from bacteria.
Eg: tetracycline
e. Vitamins production: different kinds of vitamin are produce from bacteria. Eg:
Vitamin B12 produce from Bacillus megatherium.
Negative effect of bacteria
i. Rotting of food by saprophytic bacteria.
ii. Saprophytic bacteria cause food poisoning.
iii. Denitrification: some bacteria convert nitrate of the soil to gaseous nitrogen.
iv. Diseases: maximum disease of animal and plant are caused by bacteria.
Cyanobacteria
Important characters
1. They are photosynthetic prokaryotes.
2. They have chlorophyll-a pigment.
3. They lack the flagella.
4. They do not show mitosis and meiosis cell division.
5. Sexual reproduction is absent.
6. Some cyanobacteria produce unique structures, called heterocyst which function as the
site of nitrogen fixation.
7. Reserve food material in the form of cynophycean starch.
Eg: Nostoc, Anabaena etc
Nostoc
Occurrence: it is colonial cyanobacteria, found in both aquatic and terrestrial habitat.
Vegetative structure:
Nostoc forms shining colonies. The size of the colony ranges from 1mm to 60cm. the colony
covered by a gelatinous sheath. Each gelatinous mass consist of filament. The filaments look
like bead under microscope. Filament without mucilaginous sheath is called trichome.
Trichome bears three kind of cell 1. Normal vegetative cells. 2. Akinetes formed by thicking
of vegetative cells. 3. Large thick walled, barrel shaped cells called heterocyst.






















Reproduction:
Reproduction takes place by vegetative and asexual methods.
a. Fragmentation: the colony breaks into two or more fragments by mechanical or
physiological means. Each fragment is capable to develop into new colony.
b. Akinetes: these are also called resting spore. They are larger and thick wall than
vegetative cell. They can survive in unfavorable conditions and germinate into a new
filament of Nostoc when favourable condition arises.
c. Heterocysts: they are larger, thick walled celled cells present in certain intervals of the
trichome. At the time of germination heterocyst divide into 4 cells called germiling.
Ruptures the outer wall, comes out and develops into the new filaments.


Economic importance’s of Nostoc.
1. Large colonies of Nostoc are edible.
2. It increases the nitrogen content of the soil.
3. It is helpful in reclaiming soil.
4. Nostoc benefits a numbers of plants with it is associated by fixing the nitrogen.
5. They are also used as food for several aquatic animals.

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