Salinibacter : an extremely halophilic bacterium with archaeal properties

The existence of large number of a member of the B acteroidetes in NaCl‐saturated brines in saltern crystallizer ponds was first documented in 1999 based on fluorescence in situ hybridization studies. Isolation of the organism and its description as S alinibacter ruber followed soon. It is a rod‐shaped, red‐orange pigmented, extreme halophile that grows optimally at 20–30% salt. The genus is distributed worldwide in hypersaline environments. Today, the genus S alinibacter includes three species, and a somewhat less halophilic relative, S alisaeta longa , has also been documented. Although belonging to the Bacteria, S alinibacter shares many features with the Archaea of the family H alobacteriaceae that live in the same habitat. Both groups use KCl for osmotic adjustment of their cytoplasm, both mainly possess salt‐requiring enzymes with a large excess of acidic amino acids, and both contain different retinal pigments: light‐driven proton pumps, chloride pumps, and light sensors. S alinibacter produces an unusual carotenoid, salinixanthin that forms a light antenna and transfers energy to the retinal group of xanthorhodopsin, a light‐driven proton pump. Other unusual features of S alinibacter and S alisaeta include the presence of novel sulfonolipids (halocapnine derivatives). S alinibacter has become an excellent model for metagenomic, biogeographic, ecological, and evolutionary studies.