Bacteriophage/Citable Version

A bacteriophage (from 'bacteria' and Greek φαγειν, 'to eat') is a virus that infects bacteria. The term is commonly used in its shortened form, phage. Phages are ubiquitous and can be found in all habitats populated by bacterial hosts, such as soil or the intestine of animals. One of the densest natural sources for phages and other viruses is sea water, where up to 10^6 phages per ml (or, at least, of virus-like particles)(Wommack & Colwell 2000). Whitman et al. (1998) argue that there are between 10^30 and 10^31 prokaryotic cells on our planet. If we assume numerically one virus for every prokaryote host, then we conservatively (e.g., Bergh et al. 1989) reach a total worldwide abundance of 10^30 virus-like particles.

Typically, phages consist of an outer protein shell enclosing genetic material. The genetic material can be ssRNA, dsRNA, ssDNA, or dsDNA between 5 and 500 kilo base pairs (kbp) long in either a circular or linear arrangement. Phages are usually between 20 and 200 nm in size.

History

In 1896, M. E. Hankin reported that something in the waters of the Ganges and Jumna rivers in India had marked antibacterial action against cholera and could pass through a very fine porcelain filter. In 1915, British bacteriologist Frederick Twort, superintendent of the Brown Institution of London, discovered a small agent that infects and kills bacteria. He considered the agent either 1) a stage in the life cycle of the bacteria, 2) an enzyme produced by the bacteria itself or 3) a virus that grows on and destroys the bacteria. Twort's work was interrupted by the onset of World War I, and when he returned to the Brown Institution, he spent the rest of his career trying to grow bacteriophages on artificial medium. Independently, French-Canadian microbiologist Félix d'Hérelle, working at the Pasteur Institute in Paris, announced on September 3, 1917 that he discovered "an invisible, antagonistic microbe of the dysentery bacillus". For d’Herelle, there was no question as to the nature of his discovery: "In a flash I had understood: what caused my clear spots was in fact an invisible microbe... a virus parasitic on bacteria." D'Herelle called the virus bacteriophage.

Bergh, O., K.Y. Borsheim, G. Bratbak, and M. Heldal. 1989. High abundance of viruses found in aquatic environments. Nature 340:467-468.

Whitman, W.B., D.C. Coleman, and W.J. Wiebe. 1998. Prokaryotes: The unseen majority. Proceedings of the National Academy of Sciences, USA 95:6578-6583.

Wommack, K.E. and R.R. Colwell. 2000. Virioplankton: viruses in aquatic ecosystems. Microbiology and Molecular Biology Reviews 64:69-114.