Dictionary:

bacteriophage

  (băk-tîr'ē-ə-fāj')

Also from Answers.com... Birth Control Safe and effective options.

A virus that infects and lyses certain bacteria.

Any of the viruses that infect bacterial cells. They are discrete particles with dimensions from about 20 to about 200 nanometers. A given bacterial virus can infect only one or a few related species of bacteria; these constitute its host range. Bacteriophages consist of two essential components: nucleic acid, in which genetic information is encoded (this may be either ribonucleic acid or deoxyribonucleic acid), and a protein coat (capsid), which serves as a protective shell containing the nucleic acid and is involved in the efficiency of infection and the host range of the virus.

The description of a bacterial virus involves a study of its shape and dimensions by electron microscopy (see illustration), its host range, the serological properties of its capsid, the kind of nucleic acid it contains, and the characters of the plaques it forms on a given host. Both the nucleic acid and the capsid proteins are specific to the individual virus; in the case of the capsid proteins this specificity is the basis for serological identification of the virus.

Diagram of a T4 bacteriophage.

The most striking form of phage infection is that in which all of the infected bacteria are destroyed in the process of the formation of new phage particles. This results in the clearing of a turbid liquid culture as the infected cells lyse. When lysis occurs in cells fixed as a lawn of bacteria growing on a solid medium, it produces holes, or areas of clearing, called plaques. These represent colonies of bacteriophage. The size and other properties of the plaque vary with individual viruses and host cells. See also Actinophage; Coliphage; Lysogeny; Lytic infection; Virus.

Viruses that attack bacteria, commonly known as phages. They pass through bacterial filters, and can be a cause of considerable trouble in bacterial cultures (for example milk starter cultures).

Any virus that causes lysis of host bacteria.

For more information on bacteriophage, visit Britannica.com.

Or simply phage; a virus that infects bacteria often killing them by lysis; many varieties exist, and usually each attacks only one kind of bacteria. Some bacteriophages are widely used as cloning vectors and for determining DNA sequence. Virulent DNA bacteriophages in the T series adsorb to specific receptor sites on the bacterial cell wall and inject their DNA content into the bacterium. The viral DNA usurps the machinery of the cell for the replication of viral DNA and protein which is assembled into a crop of progeny phage which are released by lysis from the cell. Called also bacterial virus.

• M13 b. — small rod-shaped, nonlytic, single-stranded DNA phage; used as a template in the Sangar dideoxy method for DNA sequence determination.
• φX174 b. — prototype of a class of phage that are small, icosahedral single-stranded DNA viruses that code for only 10 to 12 proteins and are highly dependent on the host cell for their replication.
• RNA b. — the genome is RNA instead of DNA; smallest known viruses, encode for only four proteins; they have contributed to basic studies of RNA.
• temperate b's — typified by λ phage; have a similar lytic life cycle but in addition have an alternate life cycle whereby the injected DNA becomes integrated into the cell DNA where it remains stable, behaving as a cell gene. The integrated DNA is called prophage and the bacterial cell is said to be lysogenic. The phage DNA may be induced whereby it becomes disassociated from the cell DNA and enters the lytic life cycle. Temperate phage may transfer bacterial cell DNA from one cell to another to produce a recombinant.