Difference Between Lytic and Lysogenic

The key difference between lytic and lysogenic cycle is that during the lytic cycle the host cell undergoes lysis while during the lysogenic cycle, the host cell does not undergo lysis straight away.

Viruses are infectious particles that cannot multiply on their own. They do not have a cellular structure (acellular). Since they cannot reproduce outside a living system, they are known to be ‘non-living obligate parasites’. In order to replicate, they must enter into a live cell of another organism and then undergo their multiplication process. The process of viral multiplication within the live cell is known as ‘replication’. There are two different viral replication patterns as the lytic cycle and lysogenic cycle. These patterns can also be interchangeable. Some viruses are capable of showing both these patterns. They first replicate with the lysogenic cycle and then switch to the lytic cycle.

CONTENTS

1. Overview and Key Difference
2. What is Lytic Cycle
3. What is Lysogenic Cycle
4. Similarities Between Lytic and Lysogenic Cycle
5. Side by Side Comparison – Lytic vs Lysogenic Cycle in Tabular Form
6. Summary

What is Lytic Cycle?

The lytic cycle is one of the main viral replication patterns. The viruses that show lytic cycle, first enter the host cell, replicate and then cause the cell to burst, releasing new viruses. At the beginning of the lytic cycle, the virus injects its nucleic acids (DNA or RNA) into the host cell. Then, that particular gene takes over the metabolic activities of the host cell. After that, it directs the host cell to produce more viral genes. Finally, the genes and proteins assemble within the bacterial cell and become mature viruses. That is how matured viruses come out by bursting the bacterial cell.

Therefore, as the name implies, during the lytic cycle, bacterial cell lysis occurs. Hence, the viruses that show lytic cycles are virulent than the viruses that undergo the lysogenic cycle.

What is Lysogenic Cycle?

Lysogenic cycle is the second type of replication cycle that bacteriophages or bacteria-infecting viruses show. These viruses first inject their nucleic acid into the bacterial cell and then integrate it with the nucleic acid of the host cell (DNA or RNA) and make it replicate as the host cell multiplies. And, this new set of genesis known as ‘prophage’. These types of viruses establish long term relationships with the host cell they infect. And, this relationship may alter the characteristics of the host cell, but it does not destroy the cell.

During the lysogenic cycle, bacterial cell lysis does not occur. Generally, the viruses that undergo a lysogenic cycle are not virulent.

What are the Similarities Between Lytic and Lysogenic Cycle?

• Lytic and lysogenic cycles are shown by bacteriophages during the multiplication.
• Also, viral DNA replicates within the bacterial cell in both cycles.
• Furthermore, viruses inject their DNA into bacterial cells during both cycles.

What is the Difference Between Lytic and Lysogenic Cycle?

The key difference between lytic and lysogenic cycle is that the bacterial cell lysis occurs during the lytic cycle while it does not occur during the lysogenic cycle. Moreover, in the lytic cycle, viral nucleic acids destroy the DNA or RNA in the host cell. But, in the lysogenic cycle, instead of destroying the nucleic acid of the host cell, the viral nucleic acid integrates with the DNA or RNA in the host cell. Therefore, this is a significant difference between lytic and lysogenic cycle. In the lytic cycle, the viral DNA or RNA controls the cell functions. In the lysogenic cell cycle, viral DNA or RNA makes a long term relationship with the host cell. Thus, this is also a difference between lytic and lysogenic cycle.

Unlike in the lysogenic cycle, viruses produce progeny phases in the lytic cycle. On the other hand, ‘prophage’ can only be seen in the lysogenic cycle. Moreover, in the intracellular accumulation phase of the lytic cycle, there is a combination of viral nucleic acid and structural proteins that ultimately results in viral particles. However, this process is not available in the lysogenic phase. Hence, we can consider this also as a difference between lytic and lysogenic cycle. Also, a further difference between lytic and lysogenic cycle is that the viral DNA or RNA may remain in the host cell permanently after the lysogenic cycle is completed. But, since the host cells are damaged by the viruses, there are no such remaining viral nucleic acids in the lytic cycle.

Besides, unlike the lysogenic cycle, the lytic cycle takes place within a short period. Also, the lytic cycle can be seen in many virulent virus types. On the other hand, lysogenic cycle tales place within a longer period of time and it is seen in less virulent viruses. So we can take this too as one more difference between lytic and lysogenic cycle.

Below infographic summarizes the difference between lytic and lysogenic cycle.

Summary – Lytic vs Lysogenic Cycle

Lytic and lysogenic are two modes of bacteriophage replication. During the lytic cycle, bacterial cell lyses while during the lysogenic cycle, lysis does not occur. Furthermore, virulent bacteriophages carry out lytic cycle while the less virulent bacteriophages carry out the lysogenic cycle. Moreover, the lytic cycle occurs within a short period of time while the lysogenic cycle takes place for a longer time period. The characteristic feature of the lysogenic cycle is the prophage formation. Prophage formation does not occur in the lytic cycle. Furthermore, integration of viral and bacterial DNA occurs in the lysogenic cycle while it does not occur in the lytic cycle. Thus, this is a summary of the difference between lytic and lysogenic.

Reference:

1. “Bacteriophages.” Khan Academy, Khan Academy, Available here.

Image Courtesy:

1. “Lysogentic cycle diagram” By Sseifert242 – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Lytic Cycle” By xxoverflowed (CC BY 2.0) via Flickr