The process by which virus complete their life cycle by invading and destroying bacterial cells is called the lytic life cycle. The stages of the lytic cycle of T2 phage or virulent phage are discussed.
1. Infection stage: T2 bacteriophage attaches to the cell wall of E. coli bacteria. The virus attaches to the receptive spot of the bacterium by tactile fibers. Then the tangential fibers contract. The base plate of the virus comes into contact with the cell wall of the bacteria. An enzyme called lysozyme is released from the tail of the virus. Lysozyme dissolves mucopeptides in the bacterial cell wall. As a result, a fine pore or duct is formed. This process is called drilling. Virus DNA enters the bacterial cell through pores or tubules. But the capsid coat remains outside.
2. Dormant period: Virus DNA remains inactive for 12-22 minutes after entering the host cell. During this time the DNA of the virus takes control of the genetic activity of the host.
3. Production of phage organelles: After virus DNA enters the host cell, it establishes dominance over host DNA. Then, with the help of polymerase enzymes, it uses the host nucleotides to produce new DNA. The new DNA produced makes RNA. RNA makes proteins with the help of host ribosomes. The protein molecules join together to form the capsid. Note that separate proteins are produced to form the head, tail and tangential filaments of the phage. Dr. Siddiq Publications
4. Formation of T2 Phase: Protein molecules join together to form head, tail and tangential fibers. Later these three parts join together to form the protein shell. A copy of the DNA molecule enters the brain. The tail and other parts are then joined to form the T2 phase. In this way, the bacterial cell produces numerous false virus. Finally, the synthesis of lysozyme enzyme occurs in the tail of the virus.
5. Lysis: Virus multiply inside host cells. A great stress is created in the host’s cell wall. The mucoprotein complex of the host cell wall is damaged by the action of the enzyme lysozyme. As a result, the cell wall ruptures and T2 phase is released. The breaking down of the cell wall is called lysis. Fungi of such nature are called lytic fungi or virulent fungi.
The period from when the host infects the bacterium to the formation of a full-fledged virus is called eclipse. T2 phage takes 30 minutes for virus to multiply (eclipse). During this time 300 T2 phases are generated per cell. The released new phage then invades the new host cell. Dr. Siddiq Publications