Life cycle of Bacteriophage
There are two types of life cycle of bacteriophages. Lytic cycle (Master-slave relationship)
Lysogenic cycle (Host-guest relationship)
5.2.1 Lytic Cycle (Master-slave relationship)
The lytic cycle of bacteriophage consists of the following steps.
Attachment:
In the first step, the bacteriophage attaches to the cell wall of the host that is bacterium at a specific site known as the receptor site. The attachment occurs by tail fibers.
Penetration:
The tail of virion releases an enzyme known as lysozyme which dissolves a small portion of bacterial cell wall. Now the tail sheath contracts and injects DNA into the host cell. The protein coat of the virus remains outside of the cell.
Multiplication of virion:
After entering the host cell the virion DNA takes over the control of the biosynthetic machinery of the host cell and forces the host cell to synthesize necessary viral components, i.e., DNA and protein. In this way, the virus starts multiplying. After 25 minutes of initial infection about 200 new bacteriophages are found in bacterial cells.
Lysis:
In this final step, the new daughter phages exert pressure on the bacterial cell wall and the enzyme lysozyme also attacks the cell wall from the inner side. Eventually, the cell wall bursts, and the progeny of viruses is released. This process is called lysis of bacterium. Newly formed phages are now ready to attack new hosts to start the lytic cycle again.
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