Halobacterium (common abbreviation Hbt.) is a genus in the family Halobacteriaceae. The genus Halobacterium ("salt" or "ocean bacterium") consists of several species of Archaea with an aerobic metabolism which requires an environment with a high concentration of salt; many of their proteins will not function in low-salt environments. They grow on amino acids in their aerobic conditions. Their cell walls are also quite different from those of bacteria, as ordinary lipoprotein membranes fail in high salt concentrations. In shape, they may be either rods or cocci, and in color, either red or purple. They reproduce using binary fission (by constriction), and are motile. Halobacterium grows best in a 42 °C environment. The genome of an unspecified Halobacterium species, sequenced by Shiladitya DasSarma, comprises 2,571,010 bp (base pairs) of DNA compiled into three circular strands: one large chromosome with 2,014,239 bp, and two smaller ones with 191,346 and 365,425 bp. This species, called Halobacterium sp. NRC-1, has been extensively used for postgenomic analysis. Halobacterium species can be found in the Great Salt Lake, the Dead Sea, Lake Magadi, and any other waters with high salt concentration. Purple Halobacterium species owe their color to bacteriorhodopsin, a light-sensitive protein which provides chemical energy for the cell by using sunlight to pump protons out of the cell. The resulting proton gradient across the cell membrane is used to drive the synthesis of the energy carrier ATP. Thus, when these protons flow back in, they are used in the synthesis of ATP (this proton flow can be emulated with a decrease in pH outside the cell, causing a flow of H+ ions). The bacteriorhodopsin protein is chemically very similar to the light-detecting pigment rhodopsin, found in the vertebrate retina. Species of Halobacterium Halobacterium cutirubrum > Halobacterium salinarum Halobacterium denitrificans > Haloferax denitrificans Halobacterium distributum > Halorubrum distributum Halobacterium halobium > Halobacterium salinarum Halobacterium jilantaiense Halobacterium lacusprofundi > Halorubrum lacusprofundi Halobacterium mediterranei > Haloferax mediterranei Halobacterium noricense Halobacterium pharaonis > Natronomonas pharaonis Halobacterium piscisalsi Halobacterium saccharovorum > Halorubrum saccharovoru Halobacterium salinarum Halobacterium sodomense > Halorubrum sodomense Halobacterium trapanicum > Halorubrum trapanicum Halobacterium vallismortis > Haloarcula vallismortis Halobacterium volcanii > Halobacterium volcanii Genome structure The Halobacterium NRC-1 genome is 2,571,010 bp compiled into three circular replicons. More specifically, it is divided into one large chromosome with 2,014,239 bp and two small replicons pNRC100 (191,346 bp) and pNRC200 (365,425 bp). While much smaller than the large chromosome, the