What is the Difference Between Virulent and Temperate Phage

The main difference between virulent and temperate phage is that virulent phages undergo the lytic cycle whereas temperate phages undergo the lysogenic cycle.

Virulent and temperate phages are two types of bacteriophages classified based on their life cycle. Generally, bacteriophages are viruses that infect bacterial cells. They use bacterial cells as host cells to amplify their spread in the environment.  

Key Areas Covered

1. What is Virulent Phage
   • Definition, Characteristics, Importance
2. What is Temperate Phage
   • Definition, Characteristics, Importance
3. Similarities Between Virulent and Temperate Phage
   • Outline of Common Features
4. Difference Between Virulent and Temperate Phage
   • Comparison of Key Differences

Key Terms

Temperate Phage, Virulent Phage

What is Virulent Phage

Virulent phage is one of the two types of bacteriophages that infect bacterial cells. It undergoes the lytic life cycle inside the bacterial cell. During the life cycle, after adsorption on a bacterial cell, the virulent phage injects its nucleic acids, either DNA or RNA, inside the bacterial cell. Meanwhile, the capsid of the bacteriophage remains outside the bacterial cell. While the DNA of the bacteriophage replicates inside the cell, bacterial DNA undergoes degradation. Phage protein synthesis also occurs inside the bacterial cell simultaneously. In the next stage, the progeny of virions assembles, and at the end of the life cycle, the bacterial cell releases virions.

Figure 1: Lytic Cycle

Furthermore, the infection of the virulent phages results in the destruction and limiting of the bacterial population.

What is Temperate Phage

Temperate phage is the second type of bacteriophage that infects bacterial cells. However, this type of phage undergoes a lysogenic life cycle. Usually, the lysogenic cycle is the predominant type of life cycle of bacteriophages inside the bacterial cells. In the lysogenic life cycle, the phage DNA integrates into the host cell genome. However, this type of life cycle does not involve the direct destruction of the bacterial DNA and the bacterial cell. Some other temperate phages such as Escherichia coli-specific P1 phage localize extrachromosomally in the bacterial cell.

Figure 2: Lysogenic Cycle

Temperate phages have a significant impact on individuals as well as bacterial clusters. In general, the genes of the temperate phages undergo replication along with bacterial DNA replication. But the assembly and the release of virions do not occur in the lysogenic life cycle. Therefore, infected bacterial cells do not undergo lysis. In addition, the integrated or extrachromosomal form of phage in the bacterial cell is called the prophage. Moreover, the bacterial cell with integrated prophage is called the lysogen. In the meanwhile, the lysogenic development results in the induction of stress response, which in turn initiates switching from the lysogenic to lytic cycle inside the bacterium. This destroys the infected bacterial cells.   

Similarities Between Virulent and Temperate Phage

• Virulent phage and temperate phage are two types of bacteriophages that infect bacterial cells.
• They use bacterial cells as host cells for their amplification.
• At the end of the amplification, they destroy the infected bacterial cells to spread in the environment.
• Bacteriophages are important as natural predators of bacteria.

Difference Between Virulent and Temperate Phage

Definition

Virulent phage refers to a bacteriophage that causes the destruction of the host bacterium by lysis while temperate phage refers to a bacteriophage that displays a lysogenic life cycle.

Life Cycle

Generally, virulent phages undergo a lytic life cycle while temperate phages undergo a lysogenic life cycle.

Importance

Virulent phages result in the direct destruction of bacteria while temperate phages do not result in the direct destruction of bacteria.

Significance

Virulent phage results in the limiting of the bacterial population while the lysogenic life cycle of temperate phage is the predominant life cycle of the bacteriophages.

Conclusion

In brief, virulent phage and temperate phage are the two types of bacteriophages that infect bacterial cells. More importantly, virulent phage undergoes a lytic cycle as the life cycle. Therefore, it results in the direct destruction of the bacterial cell. In contrast, temperate phage undergoes a lysogenic life cycle. Hence, it does not result in the direct destruction of the bacterial cell. Therefore, the main difference between virulent and temperate phage is their life cycle.

References:

1. Cieślik M, Bagińska N, Jończyk-Matysiak E, Węgrzyn A, Węgrzyn G, Górski A. Temperate Bacteriophages-The Powerful Indirect Modulators of Eukaryotic Cells and Immune Functions. Viruses. 2021 May 28;13(6):1013. doi: 10.3390/v13061013. PMID: 34071422; PMCID: PMC8228536.

Image Courtesy:

1. “Lytic cycle” By University of Barcelona – Own work (CC BY 3.0) via Commons Wikimedia
2. “Viral Replication” By Thinkerbug – Own Work (CC BY-SA 4.0) via Commons Wikimedia