The main difference between the two life cycles followed by the phage during the infection to the bacterium is that in the lytic phase the phage infects the machinery of the cell to make more of its components, and later they lyse, or destroy, the cell, and releases new phage particles. However, in the lysogenic phase, the phage does not destroy the host cell; instead, they insert their genetic material with the chromosome of the host cell, which replicates it as a unit.
Bacteriophage or phage or bacterial virus is also known as bacterial eater are the types of virus that infects explicitly virus, as they destroy their host cell. Bacteriophage was discovered by the two researchers independently, Frederick W. Twort in Great Britain in 1915 and Félix d’Hérelle in France in1917. D’Hérelle also coined the term bacteriophage.
The structure of the phage is simple, made up of molecules of nucleic acid, which is in a prism shape head and is surrounded by the protein capsid. The head is connected to the tail by the collar or neck region; the tail also is known as the sheath is the hollow tube-like structure. This tube helps in inserting the viral genetic material into the host cell. The tail has the attachment of the base plate, which supports in binding with the host cell.
Before the infection, the phage is involved in preparing itself by undergoing through the replication of its genetic material, and transcription and translation, to carry out growth, biosynthesis and cell division.
To transfer the genetic material, the phage needs to enter the host cell, and so they attached to the specific receptors present on the surface of the bacterial cell. They create a small hole which facilitates the transferring of the genetic material into the bacterial cellular machinery.
Further process of replication is divided into two types of phase, which are the lytic or virulent phase and lysogenic phase or temperate phase. It depends on the condition of the environment of the bacterial cell, on the base of which the phage undergoes which cycle.
In this article, we will be elaborating the points on which the two types of cycles which are lytic or lysogenic differs, with the brief description of the process of their replication.
Content: Lytic Vs Lysogenic Phase
Comparison Chart
| Basis For Comparison | Lytic Phase | Lysogenic Phase |
|---|---|---|
| Meaning | The type of viral reproduction or referred to as virulent infection, where the host cell is killed by the infecting phage to produce more of their progeny. | The type of temperate or non-virulent infection, where the viral DNA enters the host genome and does not kill it. |
| Host DNA | The viral DNA does not integrate into the host DNA in the lytic phase. | The viral DNA integrates into the host DNA in the lysogenic phase. |
| The host DNA is hydrolyzed. | The host DNA is not hydrolyzed. | |
| Genetic recombination does not occur in the host bacterium. | Genetic recombination occurs in the host bacterium. | |
| The cellular mechanism of the host cell is completely under the control of the viral genome. | The cellular mechanism of the host cell is slightly interfered by the viral genome. | |
| Viral DNA | The replication of the viral DNA occurs separately from the replication of the host DNA. | The replication of the viral DNA occurs with the replication of the host DNA. |
There is no prophage in the lytic cycle. | Prophage (set of viral genes) occurs in the lysogenic cycle. | |
| Lytic phase exhibit the symptoms of viral replication. | Lysogenic phase does not exhibit the symptoms of viral replication. | |
| The productivity is higher of the viral DNA in the lytic phase. | The productivity is lower of the viral DNA in the lysogenic phase. | |
| Time Taken | Lytic phase completes its cycle in a short time. | Lysogenic phase completes its cycle in a longer time than a lytic phase. |
Definition of Lytic Phase
In the lytic cycle or the virulent infection, the infecting phage ultimately attacks the host cell to destroy cellular machinery of the host cell and create numerous progeny of their own kind. The lytic cycle is completed in five major steps: adsorption, penetration, replication, maturation, and release of the mature viruses.
Immediately after getting attached to the cell wall of the host cell by the specific receptor, the virus weakens the cell membrane. To enter the host cell, the virus creates a hole. After injected into the host cell, the phage genome starts producing early proteins that weaken the host DNA and allow the penetration of the phage to take control over the cellular machinery of the host DNA.
The phage starts synthesizing more proteins to produce more new phage particles. During this process, the host cell weakens and eventually burst and thus releasing 100-200 new phages progeny into the environment.
Definition of Lysogenic Phase
The lysogenic cycle, also known as the temperate or non-virulent phase, is known for not killing the host cell; instead, it survives there as a refuge in a dormant form. After injecting itself into the host cell, it penetrates the host genome by the help of phage-encoded integrases. The new part of the genes in the host genome is said as a prophage.
Along with the replication of the host genome, viral DNA also gets replicates and does not require any proteins to produce its progeny.
Key Differences Between Lytic and Lysogenic Phase
Given below are the essential points to variate between lytic and lysogenic phase:
- The type of viral reproduction or referred as virulent infection, where the host cell is killed by the infecting phage to produce more of their progeny is known as lytic phase whereas the type of temperate or non-virulent infection, where the viral DNA enters the host genome and does not kill it, but replicates itself with the host genome is known as lysogenic phase.
- The viral DNA does not integrate into the host DNA in the lytic phase, though the viral DNA integrates into the host DNA in the lysogenic phase to get replicated.
- The host DNA is hydrolyzed of the lytic phase, but it is not in the lysogenic phase.
- In the lytic phase, the genetic recombination does not occur in the host bacterium, but in lysogenic phase, the genetic recombination occurs in the host bacterium.
- The cellular mechanism of the host cell is completely under the control of the viral genome in the lytic phase; however, the cellular mechanism of the host cell is slightly interfered by the viral genome.
- In the lytic phase, the replication of the viral DNA occurs separately from the replication of the host DNA, whereas in lysogenic phase the replication of the viral DNA occurs with the replication of the host DNA.
- Prophage (set of viral genomes) occurs in the lysogenic cycle, but the productivity of the progeny is lower as compared to the lytic phase.
- Lytic phase completes its cycle in a short time than the lysogenic phase.
Conclusion
Bacteriophages also infect the single-celled prokaryotic organisms known as archaea. It is might possible that every bacterium is infected by one or more viruses known as bacteriophages, though most research has been done on the bacteriophages that infect the E. coli like phage lambda and T-phages.
However, in this content, we came to know about the two types of infection caused by the virus ‘bacteriophage’ and their mechanism of replication inside the host cell.
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