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bacteriophage

bacteriophage (băktēr´ēəfāj´), virus that infects bacteria and sometimes destroys them by lysis, or dissolution of the cell. Bacteriophages, or phages, have a head composed of protein, an inner core of nucleic acid—either deoxyribonucleic acid (DNA) or ribonucleic acid (RNA)—and a hollow protein tail. A particular phage can usually infect only one or a few related species of bacteria; for example, coliphages are DNA-containing viruses that infect only the bacterium Escherichia coli.

A virus infects a bacterial cell by first attaching to the bacterial cell wall by its tail. In coliphages the tail is a complex protein structure consisting of a hollow contractile sheath, with a plate at the base that contains long protein fibers. The tail fibers fix the base plate to the specific receptor site on the bacterial cell wall, and the tail sheath contracts like a syringe, forcing the DNA that is inside the virus through the cell wall and cell membrane. The entire virus protein coat remains outside the bacterium.

The injected nucleic acid is the viral genetic material; it makes use of the bacterium's chemical energy and biosynthetic machinery to produce viral enzymes, as well as more phage nucleic acid. The viral proteins and nucleic acid molecules within the bacterial host assemble spontaneously into up to a hundred new phage particles. Eventually the bacterium lyses, releasing the particles. Lysis can be readily observed in bacteria growing on a solid medium, where groups of lysed cells appear as clear areas, or plaques.

Some DNA phages, called temperate phages, only lyse a small fraction of bacterial cells; in the remaining majority of the bacteria, the phage DNA becomes integrated into the bacterial chromosome and replicates along with it. In this state, known as lysogeny, the information contained in the viral nucleic acid is not expressed. A lysogenic bacterial culture can be treated with radiation or mutagens, inducing the cells to begin producing viruses and lyse. Lysogenic phages resemble bacterial genetic particles known as episomes. Incorporated phage genes are sometimes the source of the virulence of disease-causing bacteria.

The bacteriophage was discovered independently by the microbiologists F. W. Twort (1915) and Félix d'Hérelle (1917). The phages have been much used in the study of bacterial genetics and cellular control mechanisms largely because the bacterial hosts are so easily grown and infected with phage in the laboratory. Phages were also used in an attempt to destroy bacteria that cause epidemic diseases, but this approach was largely abandoned in the 1940s when antibacterial drugs became available. The possibility of "phage therapy" has recently attracted new interest among medical researchers, however, owing to the increasing threat posed by drug-resistant bacteria. In 2006 the Food and Drug Administration approved the use of bacteriophages that attack strains of Listeria as a food additive on ready-to-eat meat products.

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"bacteriophage." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. 14 Dec. 2017 <http://www.encyclopedia.com>.

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bacteriophage

bacteriophage (phage) A virus that is parasitic within a bacterium. Each phage is specific for only one type of bacterium. Most phages (virulent phages) infect, quickly multiply within, and destroy (lyse) their host cells. However, some (temperate phages) remain dormant in their hosts after initial infection: their nucleic acid becomes integrated into that of the host and multiplies with it, producing infected daughter cells (see lysogeny). Lysis may eventually be triggered by environmental factors. Phages are used experimentally to identify bacteria, to control manufacturing processes (such as cheese production) that depend on bacteria, and, because they can alter the genetic make-up of bacterial cells, they are important tools in genetic engineering as cloning vectors. See lambda phage.

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bacteriophage

bacteriophage (phage) (bak-teer-i-oh-fayj) n. a virus that attacks bacteria. The phage grows and replicates in the bacterial cell, which is eventually destroyed with the release of new phages. Each phage acts specifically against a particular species of bacterium. This is utilized in phage typing, a technique of identifying bacteria by the action of known phages on them.

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bacteriophage

bacteriophage (phage) A type of virus which infects bacteria. Infection with a bacteriophage may or may not lead to the death of the bacterium, depending on the phage and sometimes on conditions. A given bacteriophage usually infects only a single species or strain of bacterium. Phages can be found in most natural environments in which bacteria occur.

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bacteriophage

bacteriophage(phage) A type of virus which infects bacteria. Infection with a bacteriophage may or may not lead to the death of the bacterium, depending on the phage and sometimes on conditions. A given bacteriophage usually infects only a single species or strain of bacterium. Phages can be found in most natural environments in which bacteria occur.

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bacteriophage

bac·te·ri·o·phage / bakˈti(ə)rēəˌfāj/ • n. Biol. a virus that parasitizes a bacterium by infecting it and reproducing inside it.

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"bacteriophage." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. 14 Dec. 2017 <http://www.encyclopedia.com>.

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bacteriophage

bacteriophage 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).

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bacteriophage

bacteriophage Virus that lives on and infects bacteria. It has a protein head containing a core of DNA and a protein tail. Discovered in 1915, it is important in the study of genetics.

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