3 different types of phages and their functions

Did you know that there are 10 times more phages than bacteria? If phages where the size of a beetle, they would even cover the earth in a blanket of several miles in depth. But what kinds of phages exist on our planet? And why are they so important?

Phages are viruses that infect bacteria and they can be found literally everywhere. To understand why phage research is so important, we have to take a look at the different types.

Virulent Phages

The virulent phage, sometimes also called "lytic", infects its target and starts its reproduction immediately by mobilizing the resources of the host in its favor.

The viral genes are then expressed in a very precise and closely regulated order. The first proteins produced, the early proteins, are responsible for phage multiplication and, in many cases, interrupt the synthesis of cellular proteins. Some virulent phages are even capable of degrading the host genome and monopolizing cellular metabolism for their own reproduction.

Late proteins are essentially structural and serve to assemble capsids and to encapside the new

genomes. Once the new particles are formed, a number which varies widely according to the type of

phage, the bacterium is lysed by viral proteins that degrade the cell wall. The viruses thus released can initiate a new cycle of infection.

Filamentous Phages

When nucleic acid (generally single-stranded) is injected into the target cell, the capsid proteins are

inserted. Once inside the host, the genome is abundantly replicated and the genes necessary for the synthesis of structural proteins are expressed.

The proteins will in turn enter the cytoplasmic membrane and, together with the structural proteins inserted in the membrane, will form new capsids. The phages are then secreted through the cell wall via a channel formed of three viral protein species according to a process consuming ATP.

Unlike other types of phage, filamentous phages do not kill their host, but are released as

they replicate. This interesting characteristic makes it the tools of choice in molecular



In most cases, viral DNA integrates physically into the host genome and is copied with the entire genome as the cells divide.

This state may persist for several generations and the host cell is then said to be lysogenic. The quiescent state is maintained by a repressor of the lytic functions. Its role is to ensure the stability of the prophage state and at the same time to enable it to enter the active phase

rapidly when circumstances demand it.

This is the case when the bacterium is exposed to a deficiency or stress damaging its integrity for example. The prophage then comes out of its quiescent state and activates its replicative cycle like the virulent phages.

R.E.D. Laboratories is offering the Phelix Phage test. 

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