A A hollow sheath extends from the

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.

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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.The bacteria is now brainwashed. Instead of reading its own DNA and reproducing itself, the bacteria reads the viral DNA and begins producing bacteriophage parts. Again, like something out of a zombie story, inside the bacteria, these phage parts assemble into new bacteriophages. Soon, the bacteria is filled with viruses and is literally about to burst.Clearly this process cannot continue indefinitely, since the bacteria is ballooning with up to 1000 brand new bacteriophages! As it swells, it can no longer hold them inside, and the bacteria bursts.

This process is called lysis. Each new virus can now infect more bacteria, and the viruses will have destroyed the entire bacterial colony in no time at all.Temperate phages accomplish this process a bit differently. These phages also land on the bacteria and inject their own DNA. However, it’s typical in these cases for the viral DNA to be integrated into the bacterial DNA. Thus, the viral DNA is passed onto future generations of bacteria as the bacteria reproduce.

This process is called lysogeny.

Phage Therapy

A medical treatment known as phage therapy has been developed as an alternative to treating bacterial infections with antibiotics. Phages that are known to target particular bacteria can be introduced to the body with the intent of killing the bacterial colony that is causing infection. With the growing concern for antibiotic-resistant bacteria, phage therapy may be one solution.

Lesson Summary

A bacteriophage is a type of virus that attacks only bacteria.

It uses the bacteria to reproduce itself. Bacteriophages work by injecting their own DNA into bacterial cells. They use the biological machinery of the bacteria to reproduce, and many more viruses are created this way.There are two types of bacteriophages: those that are virulent and those that are temperate.

Virulent bacteriophages kill their host bacterial cell by causing it to go through lysis, or burst. T-phages are examples of virulent phages. Temperate bacteriophages do not kill their host but use it to reproduce itself by a process called lysogeny. Lambda phages are an example of temperate phages.


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