Haloquadra
Encyclopedia
Haloquadratum is a genus of the family Halobacteriaceae
. The first species to be identified in this group, Haloquadratum walsbyi, is highly unusual since its cells are shaped like flat, square boxes.
First 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 to 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 micrometre
s.
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.
Its mode of metabolism is not completely known; complete genetic information will give researchers necessary insight.
Halobacteriaceae
In taxonomy, the Halobacteriaceae are a family of the Halobacteriales in the domain Archaea.- Overview :Halobacteriaceae are found in water saturated or nearly saturated with salt. They are also called halophiles, though this name is also used for other organisms which live in somewhat less...
. The first species to be identified in this group, Haloquadratum walsbyi, is highly unusual since its cells are shaped like flat, square boxes.
First discovered in 1980 by A.E. Walsby
A.E. Walsby
Anthony Edward Walsby, BSc, PhD, FRS, is the Emeritus Professor of Microbiology at the School of Biological Sciences, University of Bristol....
in the Gavish Sabkha, a coastal brine pool
Brine pool
Brine pools are large areas of brine on the ocean basin. These pools are bodies of water that have a salinity three to five times greater than the surrounding ocean. For deep-sea brine pools, the source of the salt is the dissolution of large salt deposits through salt tectonics...
on the Sinai Peninsula
Sinai Peninsula
The Sinai Peninsula or Sinai is a triangular peninsula in Egypt about in area. It is situated between the Mediterranean Sea to the north, and the Red Sea to the south, and is the only part of Egyptian territory located in Asia as opposed to Africa, effectively serving as a land bridge between two...
in Egypt, this archaeon was not cultured until 2004. While attempting to culture Haloquadratum walsbyi, researchers isolated Haloarcula
Haloarcula
In taxonomy, Haloarcula is a genus of the Halobacteriaceae.- Description and Significance :Haloarcula are extreme halophilic archaeons. They are distinguished from other genera in the Halobacteriaceae family by the presence of specific derivatives of TGD-2 polar lipids...
quadrata, which has "predominantly square-shaped, somewhat pleomorphic, flat cells" , but this organism is genetically quite different to 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
Halophile
Halophiles are extremophile organisms that thrive in environments with very high concentrations of salt. The name comes from the Greek for "salt-loving". While the term is perhaps most often applied to some halophiles classified into the Archaea domain, there are also bacterial halophiles and some...
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 micrometre
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
s.
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
Halite
Halite , commonly known as rock salt, is the mineral form of sodium chloride . Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, pink, red, orange, yellow or gray depending on the amount and type of impurities...
, and then to a concentrated magnesium chloride
Magnesium chloride
Magnesium chloride is the name for the chemical compounds with the formulas MgCl2 and its various hydrates MgCl2x. These salts are typical ionic halides, being highly soluble in water. The hydrated magnesium chloride can be extracted from brine or sea water...
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; before then it had been considered to be an unculturable organism.Genome structure
The mapping of Haloquadratum walsbyis genome has been completed, giving a better understanding of the organism's genealogy and taxonomy, and the role it plays in the ecosystem. A genomic comparison of the Spanish and Australian isolates (strains HBSQ001 and C23T) strongly suggests a rapid global dispersion, as they are so similar and have retained gene order (synteny).Cell structure and metabolism
Haloquadratum walsbyi has a unique cell shape--that of an extremely thin square, its best-known characteristic. The cells possess an abundance of intracellular refractile bodies known as gas vacuoles- vacuoles filled with gas which provide buoyancy- maintaining upper position in the water column. Individual square cells are joined with others to form large sheets, sometimes as large as 40 microns. These sheets are extremely fragile and the connections between the cells are easily broken.Its mode of metabolism is not completely known; complete genetic information will give researchers necessary insight.