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The Mollicutes are a class of bacteria〔() "Mollicutes", from Encyclopædia Britannica Online. Retrieved 15 Oct. 2011.〕 distinguished by the absence of a cell wall. The word "Mollicutes" is derived from the Latin ''mollis'' (meaning "soft" or "pliable"), and ''cutis'' (meaning "skin"). Individuals are very small, typically only 0.2–0.3 μm in size and have a very small genome size. They vary in form, although most have sterols that make the cell membrane somewhat more rigid. Many are able to move about through gliding, but members of the genus ''Spiroplasma'' are helical and move by twisting. The best-known genus in Mollicutes is ''Mycoplasma''. Mollicutes are parasites of various animals and plants, living on or in the host's cells. Many cause diseases in humans, attaching to cells in the respiratory or urogenital tracts, particularly species of ''Mycoplasma'' and ''Ureaplasma''. Phytoplasma and ''Spiroplasma'' are plant pathogens associated with insect vectors. Whereas formerly the trivial name "mycoplasma" has commonly denoted any member of the class Mollicutes, it now refers exclusively to a member of the genus ''Mycoplasma''. ==Origin and development to parasitic life== Analysis of the genomes of mycoplasmas gives solid support for the hypothesis that mycoplasmas have developed from Gram-positive bacteria by a process of reductive evolution. By adopting a parasitic mode of life with use of nutrients from their hosts, mycoplasmas were able to reduce their genetic material considerably. On the other hand, mycoplasma lost the genes for many assimilative processes. Thus, Mycoplasma possibly became the smallest self-replicating organism in nature. ''Mycoplasma genitalium'', with 580,000 base pairs, has an especially small genome size. Some phytoplasmas also have a very small genome size. The genera with the smallest genome are considered to be phylogenetically the most "recent" mollicutes. To maintain their parasitic mode of life the mollicutes have developed rather sophisticated mechanisms to colonize their hosts and resist the host immune system.〔Shmuel Razin, David Yogev and Yehudith Naot (''Molecular Biology and Pathogenicity of Mycoplasmas'' ). Micr. and Molec. Biology Reviews, December 1998, pp. 1094–1156, Vol. 62, No. 4〕 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「mollicutes」の詳細全文を読む スポンサード リンク
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