Bacteriophages, often called phages, are viruses that infect bacteria. They consist of a protein coat surrounding a DNA or RNA genome and cannot replicate outside a bacterial host. Phages attach to specific receptors on a bacterium and inject their genetic material to begin infection.
Explanation
Once inside the bacterium, a phage follows either a lytic or lysogenic cycle. In the lytic cycle, the viral genome directs the host machinery to make new viral particles; these assemble and burst out of the cell, destroying it. In the lysogenic cycle, the phage integrates its genome into the bacterial chromosome and replicates along with the host until conditions trigger a switch to the lytic cycle. Phages are highly specific, often infecting only certain species or strains. They are incredibly abundant; estimates suggest that about 10³31 phage particles exist globally, making them the most common biological entities. By regulating bacterial populations, phages play a key role in nutrient cycles and microbial ecology. Researchers isolate phages using culture techniques and characterise them by morphology, genome sequence and host range.
Historical and Practical Notes
Phages were independently discovered by Frederick Twort in 1915 and Félix d’Herelle in 1917. They were used as therapeutic agents to treat infections in the early twentieth century, particularly in Eastern Europe. Interest in phage therapy has revived as a potential alternative to antibiotics against drug‑resistant bacteria. Phages are also tools in molecular biology; lambda phage vectors have been used in cloning, and phage display techniques allow the study of protein–protein interactions.
Phages influence bacterial evolution through transduction and remain a subject of intense research for their ecological impact and therapeutic potential.
Related Terms: Virus, Bacteria, Bacteriology, Phage Therapy, Bacteriostatic