A bacteriophage undergoes two types of cycle inside a host bacterium.

A bacteriophage undergoes two types of cycle inside a host bacterium.

• Lytic Cycle : In this type, the bacteriophage undergoes the normal cycle of adsorption with the help of its tail piece, then injection of genetic material, replication, and assembly of new phage particles and lysis of the host cell to release numerous progeny viruses which are exact clones of each other. Such viruses which induce lytic cycle are called virulent phages.
• Lysogenic Cycle : After infection, the bacterial DNA is not destroyed; instead, the phage releases its DNA into host which then incorporates itself within the bacterial DNA. The phage DNA gets attached to the bacterial DNA in a specific manner and replicates along with the bacterial DNA. In this condition, it is transmitted to the progeny of bacteria. Such a virus is called provirus or prophage.
• Bacteria which carry prophage are termed Lysogenic bacteria and the virus whose chromosomes become prophages are called Lysogenic viruses. The Lysogenic viruss under certain circumstances may bring about lysis of the host.