Bacteriophage: The virus that infects bacteria
What comes to your mind when you hear about bacteria and viruses? Human infections, right? Well, you will be surprised to know that there’s a type of virus that infects bacteria too. No, we aren’t joking! These viruses are known by the name ‘phage’ or ‘bacteriophage’.
A bacteriophage is a type of virus that specifically infects bacteria instead of plants, animals or humans. It was first discovered in 1915 by William Twort and have ever since played a pivotal role in viral biology or virology. In 1917, Felix d'Herelle, a French microbiologist, realized that they have the power to infect bacteria.
On one hand, bacteriophages happen to be the most studied virus, while on the other hand, their study can be extraordinarily complex. In fact, the study and use of bacteriophages has revealed that viruses primarily have two life cycles: lytic cycle and lysogenic cycle. Here’s more about the virus that infects bacteria.
What are bacteriophages made up of?
A bacteriophage is a type of virus that is made up of DNA (multi-stranded part of a living being that carries genetic information) or RNA (Ribonucleic acid, that is present in all living cells and has structural similarities to DNA). However, it is single-stranded, and is enclosed within a shell made of protein. This protein shell, also known as ‘capsid’, is present to offer protection to the viral genome (complete genetic information of an organism). A popular bacteriophage is T4, that infects the bacterium named E. coli. T4 is made up of a fibre-based protein shell that helps the virus infect the host.
Types of bacteriophages
There are two kinds of bacteriophages, namely, virulent or the killer bacteriophage and the temperate or the non-killer bacteriophage. Here’s understanding each one in details.
Virulent bacteriophage: As some of you might know, a killer virus that infects and then destroys the host cells completely is known as virulent. Therefore, in this case, a virus that kills a bacterium is called a virulent bacteriophage. This kind of bacteriophage reproduces through the lytic cycle. Here, the bacteriophage infects the bacteria by attaching to its cell wall and injecting its DNA through the wall. This DNA further replicates, unites and infects its host cell. Eventually, this results into the destruction of the host bacteria. This whole process can be completed by the virus within a meagre 20 to 30 minutes Since the rate of bacteriophage’s replication is faster than other viruses, entire colonies of bacteria can be destroyed within few minutes!
Temperate bacteriophage: As opposed to the killer virulent bacteriophages, there is also a non-killer virus known as temperate bacteriophage or prophage, that is able to reproduce without killing its host cell. This kind of bacteriophage reproduces through the lysogenic cycle. Here, the bacteriophage infects the bacteria by inserting the viral DNA through genetic recombination (rearrangement of DNA sequences by breakage and re-joining of chromosomes). However, the prophage remains dormant or inactive unless and until the bacteria that it infects reproduces. So, simply put, here the attacker and the host replicate together. As a result, the speed is a lot slower. In fact, it can often take the prophage months or even years to infect a bacterium fully. Thus, in rare cases only do they turn virulent.