T4 Bacteriophage | History, Structure, Life Cycle 2022

T4 Bacteriophage or simply phages are the type of viruses that attacks bacteria. The bacteriophages are among the most complex viruses.

They have a complex shape like a tadpole i.e., bacteriophage T4, which attacks Escherichia coli (bacterium).

History of Bacteriophage

The t4 bacteriophage was first discovered by Frederick Twort and Felix Herelle in great Britain and in France in the years 1915 and 1917.

The term bacteriophage was coined by D. Herelle. It is made of two words “Bacterio” which means bacteria and “Phage” which means eater, thus calling it bacteria eater.

T4 Bacteriophage Structure

The bacteriophages are of complex nature. That’s why the t4 bacteriophage structure is divided into main three portions in order to understand the function of different parts:

  1. Head and Tail
  2. Base Plates
  3. Spikes and Genetic Material

T4 Bacteriophage Diagram

bacteriophage-structure
Bacteriophage Structure

Head and Tail in Bacteriophage

The complexity increases because of their unique head and tail. Firstly, the head has been explained as an icosahedron which is elongated with 1250 A° (length) and 850 A° (width).

The head membrane or head envelope is made of the major protein. That major protein itself is constructed of some 2000 similar sub-units.

The tail is attached through a neck and collar to the head from one of the points.

Base Plates in Phages

The naked tail has a rather intriguing structure called a distal hexagonal base plate. This base plate is further attached to an inner cylinder hollow inside, known as the core.

This is the route or passageway from which DNA passes on its way into the host cell.

144 sub-units of the contractile sheath are found around the core in a hollow cylindrical arrangement and each consisting of 24 rays of six subunits.

Spikes and Genetic Material of Phages

Joined to the apices of the base plates are six shore spikes and six long (1300 A°) kinked tail fibers.

Encapsulated in each head envelope is a linear double-stranded DNA molecule, the genetic material of the phage, which is 53μ by 2. There is a basic problem with virus replication.

In order to produce more essential components of the virus particle, the virus must somehow induce a living cell and these components must be assembled in the proper order.

And now to infect other cells the virus particle has to escape from the cell.

T4 Bacteriophage | Lambda Phage Life Cycle

The general life cycle of a t4 bacteriophage is described graphically below:

life-cycle-of-a-bacteriophage
Life Cycle of a Bacteriophage

Phage Therapy

Well, after the discovery of Twort and Herelle. Both of them started to utilize the phages in the treatment of bacterial diseases caused in humans i.e. cholera and bubonic plague.

But, unfortunately, the phage theory was not successful or it gets credited that much. And after the discovery of antibiotics in the year 1940 it was left in the pages of history.

Now, with an increase in the resistance of bacteria against antibiotics, the therapeutic potential of these bacterial viruses has received a lot of attention.

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