What are Phages?
- Chloe Kim
- 5 days ago
- 4 min read
What are "Phages"?
Phages, also known as Bacteriophages, are viruses that infect and replicate only in bacterial cells. Although these viruses are not well known to most, they are recognized as the earth's most abundant biological agent. These phages are extremely diverse in many different factors including size, morphology, and genomic organization. Yet, despite the naturally occurring diversity, all phages consist of a "nucleic acid genome encased in a shell of phage-encoded proteins". The function of this genome is to protect its genetic material and components to transfer them to its next host. Similar to all types of viruses, phages are specific with their host species and infects only one bacterial species. Once the phage comes into contact with its host, it proceeds with 1 of 2 replication strategies: lytic or lysogenic.
Biological Agent - Microorganisms, viruses, toxins, or other biological substances that can cause disease or harm in humans, animals, or plants.
Structure of a Phage
Although there are many different types of phages, their base structure is all the same.
Capsid head --> The capsid head serves to protect the viral genome, or the DNA. It provides a protective shell which protects the DNA or RNA from harmful environmental factors like temperature changes, radiation, and other threats that could degrade the genetic material.
Collar --> The collar plays a role in regulating the attachment of the tail fibers and preventing infection under possible unfavorable conditions. The collar acts as an molecular sensor which retracts the tail fibers when the conditions aren't optimal for a successful infection.
Tail sheath --> The tail sheath allows for the phage's DNA to be delivered into the host cell.
Basal plate --> The basal plate of a phage is a multi-protein structure which plays an important role in the infection process of the host cell. It is able to control the following: host cell recognition and attachment, signaling and tail sheath contraction, and cell wall penetration and DNA injection.
Tail fibers --> The tail fibers are responsible for attaching the phage to a specific bacterial host cell. They act similar to a grappling hook which binds to the receptors of the host cell's surface.
Spikes --> The spikes are able to penetrate the bacterial cell wall and membrane to facilitate the injuection of the phage's DNA into the host cell.
Lytic and Lysogenic Replication
During either methods of replication, the phage will attach to a host bacterium and introduce its genome to the cytoplasm of the host cell. After this process, the differentiation between lytic and lysogenic replication shows:
Lytic Replication Cycle
Once the host bacterium receives the genome of the phage, it (the phage) utilizes the host's ribosomes to create proteins with the virus's genome code. This results in resources produced by the host cell to be converted into viral genomes and capsid proteins which leads to the creation of multiple copies of the original phage. Eventually, when the host cell dies, it is either actively or passively lysed (breaking down/open) which releases the phage to attach and infect another host cell.
Lysogenic Replication Cycle
On the other hand, once the phage's genome in introduced into the host cell, the phage genome is integrated into the bacterial cell's chromosome or maintained as an episomal element where it is replicated and passed on to daughter bacterial cells without killing the host. Integrated phage genomes are termed as 'prophages' which can later convert into a lytic replication cycle and kill their host- most of the time due to a change in environmental conditions.
Phage Therapy
To relate to real world issues, phages have been integrated into healthcare. Phage therapy (PT) provides a different approach to fighting bacteria as an alternative for antibiotics. According to the CDC, more than 2.8 million antimicrobial-resistant infection occur each year in the U.S. As the rates of antibiotic resistance rise and spread across communities, its more crucial than ever to begin implementing alternatives to treating bacterial infections.
Phage therapy involves the use of live lytic, bioengineered, phage-encoded biological products in combination with chemical antibiotics to treat bacterial infections. This treatment is still undergoing its experimental phase, yet still rapidly growing in its usage due to its ability to be more specific when targeting malicious bacteria cells in comparison to other methods of treating bacterial infections- like antibiotics.
Conclusion
Phages, or Bacteriophages, are still in need of further clinical research in order to be completely implemented into the healthcare world. However, lots of positive results and findings are being discovered to present day. So, phages are on their way to create a difference in the field of treating bacterial infections!
Works Cited
Assessed and Endorsed by the MedReport Medical Review Board
