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bacteriophage (bak-ter´e-o-faj)

A virus with specific affinity for bacteria, and the active agent in d'Herelle's phenomenon. B.'s have been found in association with essentially all groups of bacteria, including the Cyanobacteria; like other viruses they contain either (but never both) RNA or DNA and vary in structure from the seemingly simple filamentous bacterial virus to relatively complex forms with contractile "tails"; their relationships to the host bacteria are rather specific and, as in the case of temperate b., may be genetically intimate. B.'s are named after the bacterial species, group, or strain for which they are specific, e.g., corynebacteriophage, coliphage; a number of families are recognized and have been assigned provisional names: Corticoviridae, Cystoviridae, Inoviridae, Leviviridae, Microviridae, Myoviridae, Plasmaviridae, Podoviridae, Styloviridae, and Tectiviridae. See also coliphage.phage; [bacterio- + G. phago, to eat]
defective b. a temperate b. mutant whose genome does not contain all of the normal components and cannot become fully infectious virus, yet can replicate indefinitely in the bacterial genome as defective probacteriophage; many defective b.'s are mediators of transduction.defective phage;
filamentous b. a b. that is rod-shaped and elongated lacking the head-and-tail structure characteristic of many b.'s.
mature b. the complete, infective form of b.
temperate b. b. whose genome incorporates with, and replicates with, that of the host bacterium; dissociation (and resultant development of vegetative b.) occurs at a slow rate resulting occasionally in lysis of a bacterium and release of mature b., thus rendering the bacterial culture capable of inducing general lysis if transferred to a culture of a susceptible bacterial strain.
typhoid b. b. specific for Salmonella typhi.
vegetative b. the form of b. in which the b. nucleic acid (lacking its coat) multiplies freely within the host bacterium, independently of bacterial multiplication.
virulent b. a b. that regularly causes lysis of the bacteria that it infects; it may exist in one or the other of only two forms, vegetative or mature; it does not have a probacteriophage form (i.e., its genome does not incorporate with that of the host bacterium), therefore it does not effect lysogenization.


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