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Key Difference – Retrovirus vs Bacteriophage

Viruses are small infectious particles which replicate only inside a living organism. They are capable of infecting almost all living organisms including animals, plants and bacteria. They are microscopic particles composed of protein capsids and DNA or RNA genome. The genome of the virus can be either DNA or RNA, single stranded or double stranded, circular or linear. According to the Baltimore classification system, viruses can be classified into seven groups based on the type of the genome they possess. Retrovirus and bacteriophage are two important categories of virus. The key difference between retrovirus and bacteriophage is that retrovirus is a group of virus which contains a positive sense single-stranded RNA genome and is able to replicate via an intermediate of DNA while bacteriophage is a bacteria-infecting virus which contains either DNA or RNA genome.

1. Overview and Key Difference
2. What is Retrovirus
3. What is Bacteriophage
4. Side by Side Comparison – Retrovirus vs Bacteriophage
5. Summary

What is Retrovirus?

Retrovirus is a viral group which possesses a positive sense single-stranded RNA genome. They contain an enzyme called reverse transcriptase and their replication occurs via a DNA intermediate. The production of an intermediate DNA during the replication is unique to this group of viruses.

During the infection, retroviruses attach with host cell through the specific glycoproteins located at the outer surface of the viral particle. They fuse with the cell membrane and enter into the host cell.  After penetration into the host cell cytoplasm, retrovirus reverse transcribes its genome into double-stranded DNA using reverse transcriptase enzyme. The new DNA incorporates into host cell genome using an enzyme called integrase. Though the infection occurs, host cell fails to recognize viral DNA after integration. Hence, during the host genome replication, viral genome replicates and produces necessary proteins to make new copies of viral particles.

Human immunodeficiency virus (HIV) and human T-cell leukemia virus (HTLV) are common human retroviruses. HIV causes disease AIDs, and HTLV causes leukemia.

Due to their natural ability to insert the viral genome inside the host organisms, retroviruses are used in gene delivery systems, and they are considered as valuable research tools in Molecular Biology.

Difference Between Retrovirus and Bacteriophage

Figure 01: HIV replication

What is a Bacteriophage?

A bacteriophage (phage) is a virus which infects and propagates within a specific bacterium. They are also known as bacteria eaters since they act as bactericidal agents. Bacteriophages were discovered by Frederick W. Twort in 1915 and named as bacteriophages by Felix d’Herelle in 1917.  They are the most abundant viruses on the earth. They are also composed of a genome and a protein capsid. Bacteriophage genome can be either DNA or RNA. But the large majority of bacteriophages are double-stranded DNA viruses.

Bacteriophages are specific to one bacterium or a specific group of bacteria. They are named with the bacterial strain or the species they infect. As an example, bacteriophages which infect E coli are called coliphages. There are different shapes in bacteriophages. The most common shape that bacteriophages possess is the head and tail shape.

Bacteriophages should infect the host cell in order to reproduce. They attach tightly to bacterial cell wall using their surface receptors and inject their genetic material into the host cell. Bacteriophages can undergo two types of infection named lytic and lysogenic cycle. It depends on the type of phage. In lytic cycle, bacteriophages infect bacteria and rapidly kill the host bacterial cell by lysis. In lysogenic cycle, viral genetic material integrates with bacterial genome or plasmids and exists within the host cell for several to thousand generations without killing the host bacterium.

Phages have various applications in molecular biology. They are used to treat pathogenic bacterial strains which are resistant to antibiotics. They can also be used to identify specific bacteria in disease diagnosis.

Key Difference - Retrovirus vs Bacteriophage

Figure 02: Bacteriophage infection

What is the difference between Retrovirus and Bacteriophage?

Retrovirus vs Bacteriophage

Retrovirus is a group of virus which contains a single-stranded RNA genome. Bacteriophage is a virus which infects and replicates inside bacteria.
Presence of Reverse Transcriptase
Retrovirus contains the enzyme called reverse transcriptase. Bacteriophage does not contain reverse transcriptase.
Occurrence of Reverse Transcription
Reverse transcription occurs during viral replication Reverse transcription does not occur during the viral replication.
Production of DNA Intermediate
Retroviruses produce intermediate DNA copy of the genome. Bacteriophage does not produce DNA intermediate.

Summary – Retrovirus vs Bacteriophage

Retrovirus and bacteriophage are two types of viruses. Retrovirus is a group of viruses with positive sense single-stranded RNA genome that replicates through an intermediate DNA. Bacteriophage is a virus which attacks bacteria and replicates using bacterial replication mechanisms. Bacteriophages are the most abundant viruses in the biosphere, and they can have either DNA or RNA genomes. This is the difference between retrovirus and bacteriophage.

1. Coffin, John M. “The Place of Retroviruses in Biology.” Retroviruses. U.S. National Library of Medicine, 01 Jan. 1997. Web. 05 Apr. 2017
2. Gelderblom, Hans R. “Structure and Classification of Viruses.” Medical Microbiology. 4th edition. U.S. National Library of Medicine, 01 Jan. 1996. Web. 05 Apr. 2017
3. Hatfull, Graham F., and Roger W. Hendrix. “Bacteriophages and their Genomes.” Current opinion in virology. U.S. National Library of Medicine, 01 Oct. 2011. Web. 05 Apr. 2017
4. Coffin, John M. “Immune Response to Retroviral Infection.” Retroviruses. U.S. National Library of Medicine, 01 Jan. 1997. Web. 05 Apr. 2017

Image Courtesy:
“Hiv gross” By Translated by Raul654 – Originally from GFDL image Image: Hiv gross german.png, (CC BY-SA 3.0) via Commons Wikimedia
“Phage injecting its genome into bacterial cell” By GrahamColm at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia