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''Haloquadratum'' (''"salt square"'') is a genus of the family Halobacteriaceae.〔See the NCBI (webpage on Haloquadratum ). Data extracted from the (【引用サイトリンク】 title=NCBI taxonomy resources )〕 The first species to be identified in this group, ''Haloquadratum walsbyi'', is highly unusual since its cells are shaped like flat, square boxes. Discovered in 1980 by A.E. Walsby in the Gavish Sabkha, a coastal brine pool on the Sinai Peninsula in Egypt, this archaeon was not cultured until 2004. While attempting to culture ''Haloquadratum walsbyi'', researchers isolated ''Haloarcula quadrata'', which has "predominantly square-shaped, somewhat pleomorphic, flat cells", but this organism is genetically quite different from ''Haloquadratum'', belongs to a separate genus, and is not a dominant microbe in salt lakes. ''Haloquadratum'' are remarkable for their regular square-shaped cells and relative abundance in halophilic environments. The cells typically contain polyhydroxyalkanoate (PHA) granules as well as large numbers of refractile gas-filled vacuoles which provide buoyancy in a watery environment and may help to position the cells to maximise light-harvesting. The cells may join with others to form fragile sheets as extensive as 40 micrometres. ''Haloquadratum walsbyi'' can be found anywhere in hypersaline waters. When sea water evaporates, high concentration and precipitation of calcium carbonate and calcium sulphate result, leading to a hypersaline sodium chloride-rich brine. Further evaporation results in the precipitation of sodium chloride or halite, and then to a concentrated magnesium chloride brine termed ''bittern''. During the final stage of halite formation, before magnesium chloride concentration causes the brine to become sterile, ''Hqr. walsbyi'' flourishes and can make up 80% of the brine's biomass. == Description and significance == The archaeon ''Haloquadratum walsbyi'' ("salt squares of Walsby") was first discovered in 1980 by A.E. Walsby in the Gavish Sabkha, a coastal brine pool in the Sinai peninsula, Egypt, and formally described by Burns ''et al.'' in 2007. The "square haloarchaea of Walsby" were notable because of their extremely thin (around 0.15 μm), square-shaped structure. While this archaeon was discovered in 1980, it was not cultivated in the lab until 2004. 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「Haloquadratum」の詳細全文を読む スポンサード リンク
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