A phage, short for bacteriophage, is a type of virus that infects and replicates within bacteria. Phages are composed of genetic material (either DNA or RNA) surrounded by a protein coat. They are highly diverse in terms of their morphology, genetic makeup, and modes of infection.
Phages have a specific host range, meaning they can only infect certain bacterial species or strains. When a phage encounters a susceptible bacterial host, it attaches to the bacterial cell surface and injects its genetic material into the host cell. Once inside, the phage hijacks the host's cellular machinery to replicate its own genetic material and produce new phage particles.
Phages can follow two main life cycles: lytic and lysogenic. In the lytic cycle, the phage replicates rapidly within the host cell, ultimately causing the cell to burst (lyse), releasing new phage particles to infect other bacterial cells. In the lysogenic cycle, the phage integrates its genetic material into the host cell's genome as a prophage, replicating along with the host cell without causing immediate cell lysis. Under certain conditions, the prophage can exit the host genome and initiate the lytic cycle.
Phages play important roles in regulating bacterial populations in natural environments, as they can control bacterial abundance and diversity. They are also of interest in various fields, including biotechnology, medicine, and agriculture. In medicine, phages are being investigated as potential alternatives to antibiotics for treating bacterial infections, particularly those caused by antibiotic-resistant bacteria. Additionally, phages have applications in bioremediation, food safety, and as tools for genetic engineering and molecular biology research.