Bacteriophage: The horizontal gene transfer machine

Phage enthusiasts world is covered with the thick cloud that is still surveying scientists' heads all over the world. As phages are notoriously known to be agents of lateral transfer of genes in the bacteria, this is considered an undesirable character and limits the practicality of phage applications (including therapy). Bacteria are not the only living entities experiencing gene transfer; gene transfer is essential for genetic evolution. This process involving phages transferring genes from bacteria to bacteria is termed phage transduction. I wrote an interesting article on phage transduction that is discovering how phages contribute to horizontal gene transfer; click here to read (it will open a new window). 
Horizontal gene transfer by bacteriophages, plasmid, and transposon. Photo by Melanie Blokesch, 2015


What is horizontal gene transfer?

Horizontal gene transfer, also termed lateral gene transfer refers to an exchange of genetic materials between the organisms of different species. Transposons, plasmids, and bacteriophages are the typical agents of this type of gene transfer. The passed genes can give a new role to the recipient organism, hence playing a significant part in ecological and evolutional adaptation.

Can a lytic phage aid horizontal gene transfer?

Yes, studies have reported the lytic bacteriophage-mediated gene transfer. The accidental cut of the host genome remains a significant reason for such a scenario to happen when a prophage is induced. During the cutting of the prophage from the host chromosome, a fragment of neighboring chromosomal DNA can be accidentally excised and transferred to the new host that the phage will infect. (Marceli et al., 2020 published a very informative study on this).

What is a prophage?

As this term appeared in the previous segment, it is better to discuss it. Prophages are majorly bacteriophage genomes that are integrated into the host genome. A single bacterial genome can encode for more than one prophage, and the prophages are relatively common among the hosts.

Differences between a Bacteriophage and a prophage

Bacteriophages Prophages
They are active viruses that infect bacteria. They have lytic and lysogenic cycles. They are the latent form of bacteriophages in which the viral genome is inserted into the host chromosome.

Why is horizontal gene transfer considered harmful?

While horizontal gene transfer is considered to be bad for humans, it is, in fact, beneficial to bacteria. Most of the characters passed through this kind of transfer tend to be detrimental to our needs. Among the diseases humans are frequently encountering, bacterial infections are prevalent. Many people suffer from untreatable diseases due to some acquired genes through lateral transfer. To get a clear picture of this, let's look at how bacteria benefit from this transfer.

Effects of horizontal gene transfer to a bacteria

Some genes have no effect, but some can be very beneficial to the new host. The following are the two noticeable effects that may be caused by a horizontal gene transfer.
  • Transfer of resistance
  • Transfer of pathogenicity
  • Toxin genes transfer
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