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Subterranean salt deposits are the remains of ancient hypersaline waters that presumably supported dense populations of halophilic microorganisms including representatives of the haloarchaea (halobacteria). Ancient subterranean salt deposits (evaporites) are common throughout the world, and the majority sampled to date appear to support diverse populations of halobacteria. The inaccessibility of deep subsurface deposits, and the special requirements of these organisms for survival, make contamination by halobacteria from surface sites unlikely. It is conceivable that these subterranean halobacteria are autochthonous, presumably relict populations derived from ancient hypersaline seas that have been revived from a state of dormancy. One would predict that halobacteria that have been insulated and isolated inside ancient evaporites would be different from comparable bacteria from surface environments, and that it might be possible to use a molecular chronometer to establish if the evolutionary position of the subsurface isolates correlated with the geological age of the evaporite. Extensive comparisons have been made between the 16S rRNA genes of surface and subsurface halobacteria without showing any conclusive differences between the two groups. A further phylogenetic comparison exploits an unusual feature of one particular group of halobacteria that possess at least two heterogeneous copies of the 16S rRNA gene, the sequences of which may have been converging or diverging over geological time. However, results to date have yet to show any gene sequence differences between surface and evaporite-derived halobacteria that might arguably be an indication of long-term dormancy.

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A novel extremely halophilic archaeon was isolated from the Dead Sea. This isolate is rod shaped and, like Halobacterium sodomense, requires a relatively low level of sodium ions for growth and a very high level of magnesium; optimal growth occurs in the presence of 0.6 to 1.0 M Mg2+. The new strain resembles members of the Halobacterium saccharovorum-Halobacterium sodomense-Halobacterium trapanicum group in many physiological properties. However, the polar lipid composition of this organism is characteristic of representatives of the genus Haloferax; a sulfated diglycosyl diether is present, and the glycerol diether analog of phosphatidylglycerosulfate is absent. The G+C content of the DNA is 70 mol%. We found that on the basis of 16s rRNA sequence data our new isolate occupies a position intermediate between the position of the Halobacterium saccharovorum group and the position of the genus Haloferax and is sufficiently different from the previously described members of the Halobacteriaceae to justify classification in a new species and a new genus. We propose the name Halobaculum gomorrense gen. nov., sp. nov. for this organism; the type strain is strain DSM 9297.Halophilic archaea have been found in the Dead Sea since the first studies of the biology of the lake in the 1930s. At times these organisms are present in numbers high enough (?lo7 cells per ml) to impart a reddish color to the water. Such a phenomenon occurred in 1963 and 1964 and again in 1980 The following four genera of halophilic nonalkaliphilic archaea have been described previously: Halobacterium, Haloferax, Haloarcula, and Halococcus (9, 40). In the past enrichment cultures in which Dead Sea water or sediment was used as the inoculum have yielded isolates of at least three novel halophilic archaea, Halobacterium sodomense (29), Haloferax volcanii (27), and Haloarcula marismortui (36).A new bloom of halophilic archaea developed in the Dead Sea in the summer of 1992 (34). The results of polar lipid analyses suggested that the organism which dominated this community was related to the genus Haloferax. One major glycolipid was found in polar lipid extracts of the bacterial community collected from the Dead Sea during the bloom. This glycolipid coeluted with the major glycolipid of Haloferax volcanii and Haloferax mediterranei on both one-dimensional and two-dimensional thin-layer chromatograms (37). Moreover, phosphatidylglycerosulfate, a polar lipid present in all halophilic archaea except Haloferax species, was not detected in lipid extracts of the Dead Sea biomass.Attempts to identify the numerically dominant archaeal species in the Dead Sea samples by isolating and characterizing the bacteria that developed on agar plates or in liquid media were not very successful. The numbers obtained were typically 2 or more orders of magnitude lower than the numbers observed microscopically. The highest estimates of the numbers of culturable bacteria were obtained by preparing dilution series in a liquid medium suitable for the growth of Halobacte- ri...

Acidophilic, heterotrophic bacteria isolated from acidic mine effluent metabolised a range of aliphatic compounds. Aliphatic acids, which are normally thought to be toxic to acidophiles, were utilised as substrates for energy and growth by these bacteria. This biodegradative ability, concomitant with their tolerance of heavy metals, has demonstrated the potential for using these organisms for the bioremediation of multiply contaminated acidic wastewaters.