Bacteriophages

Bacteriophages, often referred to simply as phages, are a type of virus that infect and replicate within bacteria and archaea. The term "bacteriophage" literally means "bacteria eater," derived from the Greek bakterion, meaning "bacteria," and phagein, meaning "to devour." Phages play a critical role in microbiology, genetics, and biotechnology, due to their unique ability to transfer genetic material between bacteria in a process known as transduction.

Discovery

Bacteriophages were co-discovered independently by Frederick Twort in the United Kingdom in 1915 and by Félix d'Hérelle in France in 1917. D'Hérelle was the first to propose that phages were an infectious agent, seen as entities that had a natural role in controlling bacterial populations in the environment—a concept that forms the basis of phage therapy.

Structure

Bacteriophages exhibit a wide variety of shapes and sizes but generally consist of a nucleic acid molecule (DNA or RNA) encased within a protein structure known as a capsid. Some phages also have complex structures featuring tails and fibers, which they use to attach to host cells. The T4 phage, one of the most well-studied types, has a complex structure consisting of an icosahedral head and a helical tail, which it uses to inject its genetic material into a host cell.

Life Cycle

Bacteriophages have two main life cycles: the lytic cycle and the lysogenic cycle. In the lytic cycle, phages take over the host cell's machinery to replicate their genetic material and produce new phage particles. This process usually results in the lysis (breaking open) and death of the host cell. In the lysogenic cycle, the phage integrates its genome into the host cell's genome, where it can replicate along with the host cell for generations before becoming lytic.

Applications

1. 1. 1. Phage Therapy###

Phage therapy is the therapeutic use of bacteriophages to treat pathogenic bacterial infections. Phage therapy has been considered as an alternative to antibiotics in the face of rising antibiotic resistance. It has been used in Eastern Europe and the former Soviet Union for decades and is now gaining interest in the Western world.

1. 1. 1. Biotechnology###

In biotechnology, bacteriophages are used as tools for genetic engineering. Phage display, for example, is a technique where phages are used to evolve new proteins, including antibodies, with desirable properties.

1. 1. 1. Bacterial Genetics###

Phages have been instrumental in the study of bacterial genetics and molecular biology. They have been used to elucidate fundamental genetic concepts such as the nature of the genetic code, gene regulation, and genetic recombination.

Challenges and Future Directions

While the potential of phages in medicine and biotechnology is significant, there are challenges to their widespread adoption. These include the specificity of phages to particular bacterial strains, the potential for bacterial resistance to phages, and regulatory hurdles. Ongoing research aims to address these challenges by engineering phages with broader host ranges and reduced potential for resistance development.

See Also

• Virology
• Microbial genetics
• Antimicrobial resistance