Give a brief account on life cycle of bacteriophage
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Bacteriophage Life Cycles
The virus that infects bacteria – bacteriophages, exhibit 2 different life cycles:
1. Lytic cycle
2. Lysogenic cycle
Some bacteriophages have the ability to perform both lytic and lysogenic cycles.
Bacteriophage Morphology
The host specificity of bacteriophages is very high, thus enabling classification of bacteria on this specificity. A bacteriophage is of tadpole shape with a head and a tail. Head consists of tightly packed DNA covered by a protein coat, while tail is hollow core surrounded by contractile protein sheath.
Lytic Cycle
Phages that follow lytic cycle are known to be virulent or lytic phages. The five phases of a lytic cycle are as follows:
1. Adsorption—attachment of phages to a specific receptor site using tail fibers.
2. Penetration—hollow tube penetrates into the bacteria allowing the passage of DNA into the bacterial cell.
3. Synthesis—host machinery shuts down as directed by viral genome and viral components are synthesized.
4. Maturation and assembly—at the time of maturation, assembly of phage components (DNA, head, and tail) to form virions.
5. Release—lysis of the host cell releases the progeny phages.
The time interval between the entry of phage and appearance of first progeny phage is called eclipse phase. Example for lytic phage is T4 bacteriophage that infects E. coli bacteria.
Lysogenic cycle
Phages that follow lysogenic cycles are known as temperate or lysogenic phages. Immediate lysing of host cells does not occur in lysogenic cycle. Instead, the phage gets integrated into the host DNA and replicate along with it without causing harm or even become a plasmid. Under abnormal environmental conditions, when host cell deteriorates, the phage becomes active and enters the lytic phase and gets released. The dormant phage is known as prophage.
The time interval between the host infection and sudden rise in virus is called latent period. Example for lysogenic phage is phage lambda of E. colibacteria.
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The virus that infects bacteria – bacteriophages, exhibit 2 different life cycles:
1. Lytic cycle
2. Lysogenic cycle
Some bacteriophages have the ability to perform both lytic and lysogenic cycles.
Bacteriophage Morphology
The host specificity of bacteriophages is very high, thus enabling classification of bacteria on this specificity. A bacteriophage is of tadpole shape with a head and a tail. Head consists of tightly packed DNA covered by a protein coat, while tail is hollow core surrounded by contractile protein sheath.
Lytic Cycle
Phages that follow lytic cycle are known to be virulent or lytic phages. The five phases of a lytic cycle are as follows:
1. Adsorption—attachment of phages to a specific receptor site using tail fibers.
2. Penetration—hollow tube penetrates into the bacteria allowing the passage of DNA into the bacterial cell.
3. Synthesis—host machinery shuts down as directed by viral genome and viral components are synthesized.
4. Maturation and assembly—at the time of maturation, assembly of phage components (DNA, head, and tail) to form virions.
5. Release—lysis of the host cell releases the progeny phages.
The time interval between the entry of phage and appearance of first progeny phage is called eclipse phase. Example for lytic phage is T4 bacteriophage that infects E. coli bacteria.
Lysogenic cycle
Phages that follow lysogenic cycles are known as temperate or lysogenic phages. Immediate lysing of host cells does not occur in lysogenic cycle. Instead, the phage gets integrated into the host DNA and replicate along with it without causing harm or even become a plasmid. Under abnormal environmental conditions, when host cell deteriorates, the phage becomes active and enters the lytic phase and gets released. The dormant phage is known as prophage.
The time interval between the host infection and sudden rise in virus is called latent period. Example for lysogenic phage is phage lambda of E. colibacteria.
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