Phages are highly specific bacterial viruses that are believed to be the most abundant lifeform on the planet. Phages exhibit some degree of structural variation although; the “tailed” phage predominates, with more than 90% of phages belonging to this general structure.
Phages undergo one of two main lifecycles, the lytic cycle which culminates in the destruction of the infected cell or the lysogenic cycle which allows for the integration of the phage genome into the host and replication alongside the host. It should also be noted that integrated lysogenic phages can become lytic culminating in cell death when exposed to inducing agents such as ultraviolet light.
Both lifecycles have important roles to play in the control of bacterial populations within the environment, with the lytic cycle involved in the direct control of population numbers, while the lysogenic cycle allows for the transfer of bacterial genes between different strains.
Since their initial discovery in the early part of the 20th century, phages have been used to treat a variety of bacterial infections in humans, primarily in Eastern Europe and the former Soviet Union. However, due to the ascendancy of antibiotics, phages were largely ignored in the West. With the renewed concern over the continuing development of antibiotic resistance, phages have become an attractive prospect for the treatment of resistant bacteria. This has led to the development and approval of a number of commercial products for use within the food industry. Phages have also found roles in the study of protein interactions with other components, through display on the phage coat and also the detection of bacterial species.
