Difference Between Virulent and Temperate Phage

The key difference between virulent and temperate phage is that virulent phages kill bacteria during every infection cycle since they replicate only via the lytic cycle while temperate phages do not kill bacteria immediately after the infection since they replicate using both lytic and lysogenic cycles.

Phages or bacteriophages are viruses that infect bacteria. Viruses reproduce via two mechanisms as lytic cycle and lysogenic cycle. There are two main types of phages based on the mechanisms of infection and killing of the host bacterium: virulent phages and temperate phages. Virulent phages replicate via the lytic cycle. Temperate phages replicate via both lytic and lysogenic cycles. Virulent phages show generalized transduction, and they are capable of killing the host bacterium after each infection cycle. Temperate viruses show specialized transduction, and they do not kill the host bacterium immediately after the infection. They are able to integrate viral DNA into the bacterial chromosome and remain in the prophage stage for several bacterial generations without killing the bacterium.

CONTENTS

1. Overview and Key Difference
2. What is a Virulent Phage
3. What is a Temperate Phage
4. Similarities Between Virulent and Temperate Phage
5. Side by Side Comparison – Virulent vs Temperate Phage in Tabular Form
6. Summary

What is a Virulent Phage?

Virulent bacteriophage is a bacteriophage which kills the host bacterium by lysis. They always undergo a lytic life cycle, causing the death of host bacterium after each infection cycle. Infection of a bacterium by a virulent bacteriophage and transferring bacterial DNA to another bacterium during the second infection is known as generalized transduction. Hence, generalized transduction can be defined as the transfer of bacterial DNA from one bacterium to another bacterium by a virulent bacteriophage during the lytic cycle.

After infection, virulent phages are capable of controlling the bacterial cell mechanisms to replicate their own DNA. Viruses are also capable of degrading bacterial chromosome into small pieces and sudden disruption of the bacterial cell wall for the release of assembled phages, causing cell death.

What is a Temperate Phage?

Temperate phages are the bacteriophages that often display a lysogenic cycle. These phages can be selected between lytic and lysogenic pathways. Temperate phages carry out specialized transduction. When temperate phages infect bacteria, they are able to integrate viral DNA into bacterial chromosomes and remain in the prophage stage for several bacterial generations. Therefore, temperate phages do not lyse bacterial cells immediately after infection. During bacterial genome replication, viral DNA is subject to replication and enters new bacterial cells and survives.

Temperate phages remain dormant until induction. When the prophages are induced by certain factors, viral DNA detaches from the bacterial chromosome. Sometimes during this detachment, fragments of bacterial chromosomes get detached and remain attached to the prophage DNA. Due to induction, phages undergo lytic cycle afterwards. Viral genome replicates with attached bacterial DNA and packages inside new capsids and makes new phages. New phages release the bacterial cell by lysis.

What are the Similarities Between Virulent and Temperate Phage?

• Virulent and temperate phages are two types of bacteriophages.
• They infect bacteria and replicate using bacterial replication mechanisms.

What is the Difference Between Virulent and Temperate Phage?

Virulent phages are the bacteriophages that replicate only through the lytic cycle. Meanwhile, temperate phages are the bacteriophages that replicate through both lytic and lysogenic cycles. So, this is the key difference between virulent and temperate phage. Furthermore, virulent phages cannot integrate viral genome into a bacterial chromosome while temperate phages can integrate viral genome into the bacterial chromosome.

Moreover, another difference between virulent and temperate phage is that the virulent phages lyse the bacterial cell while the temperate phages do not lyse the bacterial cells. Also, virulent phages show generalized transduction while temperate phages show specialized transduction.

Below infographic summarizes the differences between virulent and temperate phage.

Summary – Virulent vs Temperate Phage

There are two types of bacteriophages: virulent and temperate. Phages show two types of replication: lytic or lysogenic replication. Virulent phages undergo only lytic cycle while temperate phages can choose between the lytic and lysogenic cycles. During the lytic cycle, virulent viruses do not integrate nucleic acids of the phage into the host’s genome. Directly after the replication and assembly, virulent viruses lyse the bacterial cells and come out. During the lysogenic cycle, temperate viruses integrate the nucleic acid of the bacteriophage into the host’s genome, but the bacterium does not lyse. Thus, this summarizes the difference between virulent and temperate phage.

Reference:

1. Hannah Simmons, M.Sc. “Virulent Bacteriophages And The Lytic Cycle”. News-Medical.Net, 2020, Available here.
2. “Temperate Phage”. Phage Consultants | Phageconsultants.Com, 2020, Available here.

Image Courtesy:

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