BACTERIOPHAGES

(Prepared by: Priya Prakash- 20220901007)

Bacteriophages or phages are viruses that infect bacteria. They are also known as 'Bacteria eater'. They are the most abundant organisms in the biosphere and are a ubiquitous feature of prokaryotic existence. Also they have been beneficial to scientists as tools to understand fundamental molecular biology, vectors of horizontal gene transfer and drivers of bacterial evolution, sources of diagnostic and genetic tools and novel therapeutic agents. 

                             This article describes the roles of phages in different host systems and how modeling, microscopy, isolation, genomic and metagenomic based approaches have combined to provide unparalleled insights into these small but vital constituents of the microbial world.

HISTORY OF BACTERIOPHAGES [1]

1915 – Bacteriophages were discovered by William Twort.

1917 – Felix d’Herelle discovered that bacteriophages has the ability to kill bacteria. He observed that filtrates from feces culture from dysentery patients induced transmissible lysis (disintegration of a cell. He continued research in two directions: (1) determining the biological nature of bacteriophages and (2) exploring the use of bacteriophages as a therapy to treat bacterial infections in a pre-antibiotic era.

1940 – Felix d’Herelle’s bacteriophage theory become universally accepted.

MORPHOLOGY OF PHAGES

 Hexagonal head containing nucleic acid covered by protein coat or capsid. Its 28-100nm in size.

Cylindrical tail which is hollow inside and covered by contractile sheath and terminal hexagonal baseplate. It also contains tail fibers projecting outwards from the baseplate and Tail pins.

 

How does a Bacteriophage infects Bacteria? Is it that Easy?

The illustration above depicts how a bacteriophage injects the nucleic acid into the cytoplasm of bacteria.

As the illustration above shows, bacteriophage hijacks the host cell's cellular machinery for their own replication. Now if the environmental conditions are unfavourable, they enter a lytic or virulent cycle, if not then they enter lysogenic or temperate cycle.

In lytic cycle, inside the infected cell, the phage genome replicates producing progeny bacteriophages. These rupture the bacterial cell wall and progenies are released to the adjacent cells and the lytic cycle is repeated.

In lysogenic cycle is a way of viral reproduction that involves integrating viral DNA into host DNA. Once the bacterial cell is infected, the viral DNA inserts itself, or incorporates itself into the host DNA, rather than staying separate.

One of the main difference between the lytic stage and lysogenic cycle is that lytic cycle results in the immediate formation of multiple copies of the virus. But in the lysogenic cycle, the viral DNA replicates only when the host cell does. It spreads from the host to the daughter cells. This is a slower process but benefit is that the viral DNA is safer and it can avoid detection for longer periods of time than it can in the lytic phase. 

The evolution of several toxigenic pathogens depended extensively on bacteriophage infections and exchanges of DNA. Examples include C. diphtheriae (causes diphtheria), S. pyogenes (causes strep throat and scarlet fever), and C. botulinum (causes food poisoning or botulism)[2].

So are there any Importance of these in our Life? Fortunately Yes.

1. Extensively used in genetic engineering as cloning vectors.
2. Used for natural removal of bacteria from water bodies.
3. Used to combat infections caused by antibiotic-resistant bacteria.
4. Used to eliminate superbugs that form biofilms present on implanted medical devices.
5. Used to treat ready-to-eat meats, fish, poultry, and soft cheeses with bacteriophages in order to eliminate foodborne pathogens.

 

Any future prospects?

Research on bacteriophages is reviving, with an emphasis on the phages themselves rather than their molecular processes. Some of the practical issues such as how to use phages to treat human diseases, how to get rid of phage pests in the food business, and what part they play in the development of human diseases, are being addressed. Phages are also being employed to investigate fundamental biophysical and molecular issues [3].

References

1. the Best for Last: Bacteriophages | Basicmedical Key

2. Clokie, M. R., Millard, A. D., Letarov, A. V., & Heaphy, S. (2011). Phages in nature. Bacteriophage, 1(1), 31–45. https://doi.org/10.4161/bact.1.1.14942

3. Campbell, A. The future of bacteriophage biology. Nat Rev Genet 4, 471–477 (2003). https://doi.org/10.1038/nrg1089