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The Pelagibacterales is an order in the Alphaproteobacteria composed of free-living bacteria that make up roughly one in three cells at the ocean's surface. Overall, members of the ''Pelagibacterales'' are estimated to make up between a quarter and a half of all prokaryotic cells in the ocean. Initially, this taxon was known solely by metagenomic data and was known as the SAR11 clade. It was first placed in the ''Rickettsiales'', but was later raised to the rank of order, and then placed as sister order to the ''Rickettsiales'' in the subclass ''Rickettsidae''.〔 It includes the highly abundant marine species ''Pelagibacter ubique''. Bacteria in this clade are unusually small. ''Pelagibacter ubique'' and related species are oligotrophs — scavengers — and feed on dissolved organic carbon and nitrogen.〔 They are unable to fix carbon or nitrogen, but can perform the TCA cycle with glyoxylate bypass and are able to synthesise all amino-acids, except glycine, and some cofactors. They also have an unusual and unexpected requirement for reduced sulfur. ''Pelagibacter ubique'' and members of the oceanic subgroup I possess gluconeogenesis but not a typical glycolysis pathway, whereas other subgroups are capable of typical glycolysis. Unlike ''Acaryochloris marina'', it is non-photosynthetic —as in, it does use light to increase the bond energy of an electron pair—, but possesses proteorhodopsin (incl. retinol biosynthesis) for ATP production from light. SAR11 bacteria are responsible for much of the dissolved methane in the ocean surface. They extract phosphate from methylphosphonic acid. The taxon derives its name from the type species ''Pelagibacter ubique''. However, this species has not yet been validly published and, therefore, neither the familiar or the species has official taxonomic standing. ==Subgroups== Currently the (unofficial) family is divided into five subgroups:〔Robert M. Morris, K.L.V., Jang-Cheon Cho, Michael S. Rappé, Craig A. Carlson, Stephen J. Giovannoni, Temporal and Spatial Response of Bacterioplankton Lineages to Annual Convective Overturn at the Bermuda Atlantic Time-Series Study Site" ''Limnology and Oceanography'' 50(5) p. 1687-1696.〕 * Subgroup Ia, open ocean, crown group — includes ''Pelagibacter ubique'' HTCC1062 * Subgroup Ib, open ocean, sister clade to Ia * Subgroup II, coastal, basal to Ia + Ib * Subgroup III, brackish, basal to I + II along with its sister clade IV * Subgroup IV, also known as LD12 clade, freshwater〔Salcher, M.M., J. Pernthaler, and T. Posch, Seasonal bloom dynamics and ecophysiology of the freshwater sister clade of SAR11 bacteria 'that rule the waves' (LD12). ISME J, 2011.〕 * Subgroup V, which includes alphaproteobacterium HIMB59, basal to the remainder 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「Pelagibacterales」の詳細全文を読む スポンサード リンク
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