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A bacteriophage (informally, ''phage'' ) is a virus that infects and replicates within a bacterium. The term is derived from "bacteria" and the (ギリシア語:φαγεῖν) (''phagein''), "to devour". Bacteriophages are composed of proteins that encapsulate a DNA or RNA genome, and may have relatively simple or elaborate structures. Their genomes may encode as few as four genes, and as many as hundreds of genes. Phages replicate within the bacterium following the injection of their genome into its cytoplasm. Bacteriophages are among the most common and diverse entities in the biosphere. Phages are widely distributed in locations populated by bacterial hosts, such as soil or the intestines of animals. One of the densest natural sources for phages and other viruses is sea water, where up to 9×108 virions per milliliter have been found in microbial mats at the surface, and up to 70% of marine bacteria may be infected by phages.〔Prescott, L. (1993). Microbiology, Wm. C. Brown Publishers, ISBN 0-697-01372-3〕 They have been used for over 90 years as an alternative to antibiotics in the former Soviet Union and Central Europe, as well as in France.〔BBC Horizon (1997): ''The Virus that Cures'' – Documentary about the history of phage medicine in Russia and the West〕 They are seen as a possible therapy against multi-drug-resistant strains of many bacteria (see phage therapy). Nevertheless, phages of Inoviridae have been shown to complicate biofilms involved in pneumonia and cystic fibrosis, shelter the bacteria from drugs meant to eradicate disease and promoting persistent infection.〔http://phys.org/news/2015-11-bacteria-bacteriophages-collude-formation-clinically.html〕 == Classification == Bacteriophages occur abundantly in the biosphere, with different virions, genomes and lifestyles. Phages are classified by the International Committee on Taxonomy of Viruses (ICTV) according to morphology and nucleic acid. Nineteen families are currently recognized by the ICTV that infect bacteria and archaea. Of these, only two families have RNA genomes and only five families are enveloped. Of the viral families with DNA genomes, only two have single-stranded genomes. Eight of the viral families with DNA genomes have circular genomes, while nine have linear genomes. Nine families infect bacteria only, nine infect archaea only, and one (''Tectiviridae'') infects both bacteria and archaea. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bacteriophage」の詳細全文を読む スポンサード リンク
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