Bacteriophage: Definition & Types

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  • 0:00 What Is a Bacteriophage?
  • 0:48 Anatomy of a Virus
  • 1:58 Types and How They Work
  • 4:00 Phage Therapy
  • 4:25 Lesson Summary
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Lesson Transcript
Instructor: Wendy McDougal

Wendy has taught high school Biology and has a master's degree in education.

A bacteriophage is a virus that exclusively attacks bacteria. Its sole purpose is to use the bacteria for reproduction. In this lesson, learn more about this microscopic invader and take a short quiz at the end.

What Is a Bacteriophage?

When we get sick, viruses are often to blame. It seems that viruses exist solely to make us miserable, doesn't it? But, we're not the only ones at risk of the ill effects of a virus. Unseen by our eyes is a barbaric little battle raging between viruses and another microscopic organism. Bacteria are also under siege by a type of virus doesn't make the bacteria sick, but has another goal in mind: reproduction.

This virus, known as a bacteriophage, or phage for short, cannot reproduce on its own. So, it commandeers an unsuspecting bacteria and utilizes its biological machinery to complete its own reproduction. In this lesson, we'll gain a better understanding of how the bacteriophage accomplishes this unique process

Anatomy of a Virus

So we've established that a bacteriophage is a type of virus. But, what exactly is a virus? It's important to note that viruses aren't alive, at least not technically alive. They aren't made of cells, and they don't posses other qualities of living things. This is the reason that a virus can't reproduce on its own. It simply doesn't have the required biological machinery, and so it needs to use a host cell.


So, let's take a closer look at a bacteriophage. Looking somewhat like a landing module from a spacecraft, this virus has a very basic structure. There's a head, which is essentially a protein shell containing genetic information either in the form of DNA or RNA. We'll use DNA for our example. A hollow sheath extends from the head and joins the tail fibers, which look like tiny legs.

The process by which a phage takes over its host bacterial cell is like something you might see in The Walking Dead. The basic idea is that the virus takes over the 'brain' of the bacteria. Instead of reproducing itself, the bacteria unwittingly creates replications of the virus. Becoming infected with the virus never produces good results for the bacteria.

Types of Bacteriophages and How They Work

There are two major types of bacteriophages. Virulent phages destroy their host as a result of reproduction. Examples of these include the T-phages, or T1-T7. These phages commonly infect E. coli bacteria. Temperate phages brainwash their host and take over its machinery but don't actually kill it. Examples of these phages are lambda types.

And so how does a bacteriophage accomplish this feat? Let's look at the virulent phages first. The virus lands and attaches onto the bacteria. Perched on its leg-like tails, it contracts the hollow sheath and penetrates the bacteria. Then, the phage injects its own DNA into the bacteria like a syringe injects a vaccine into a person. In addition, the phage may also inject enzymes that destroy the bacteria's own DNA.

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