The earlier validated name for the class, Halomebacteria (Cavalier-Smith,
2002), was rejected by the International Committee on Systematics of Prokaryotes (Garrity et al., 2011; Oren & Labeda, 2011). The halophiles of the family Halobacteriaceae (Gibbons, 1974), the only family within the Halobacteriales, the single order within the Halobacteria, are considered the halophiles par excellence, because virtually all of them are strictly dependent on high salt concentrations for maintaining growth and cellular integrity. Although scarce selleck compound reports recorded the presence of Halobacteriaceae at relatively low salinities (Rodriguez-Valera et al., 1979; Munson et al., 1997; Elshahed et al., 2004; Purdy et al., 2004), we consider this phenomenon as the result of their capacity to prevail in localized niches with increased salt concentration, or of their property to maintain viability for a defined time frame. However, the findings of Purdy et al. (2004) suggest that representatives of the Halobacteriaceae growing at relatively low salinities may be competitive in habitats with salinities at or just above that of seawater. Most species described grow optimally above buy Fluorouracil a concentration of 150 g L−1 salt and lyse at concentrations below 100 g L−1 (Oren, 2011b). At the time of writing (November 2011), the family
encompassed 129 species, classified based on a polyphasic approach, whose names have been validly published and classified in
36 genera (Oren, 2012). Aerobic halophilic Archaea thrive in environments with salt concentrations approaching saturation, such Pregnenolone as natural brines, alkaline salt lakes, marine solar salterns, and salt rocks of millenary age. They represent the major part of the microbiota of hypersaline soda lakes such as Lake Magadi, Kenya (an extremely alkaline lake), saltern crystallizer ponds, and the Dead Sea (Oren, 2011a). Most representatives are neutrophilic, many are alkaliphilic, and a moderately acidophilic species, Halarchaeum acidiphilum, isolated from commercial solar salt does not grow above pH 6.0 (Minegishi et al., 2010). Among the groups of methanogenic Archaea within the Euryarchaeota, there are a number of halophilic species able to grow at salt concentrations close to saturation. Taxonomically, the methanogens are grouped into five orders. The majority of known halophilic species are classified within the order Methanosarcinales, family Methanosarcinaceae (Boone et al., 2001; de la Haba et al., 2011). At the time of writing, this family comprised nine genera consisting of 30 species. Moderate and extreme halophiles are found in the genera Methanohalobium, Methanohalophilus, Methanosalsum, and Methanocalculus (Ollivier et al., 1998; Boone et al., 2001), all being strict anaerobes.