Passive electrical properties of Halobacterium species

The electrical conductivity of suspensions of two species of Halobacterium was measured at low A. C. frequency. The results obtained fromHalobacterium halobium suspensions show that the bacteria act as non-conducting particles. In contrast, the cells of a Halobacterium obtained from the Dead Sea (Halobacterium marismortui) had an apparently high conductivity which can be explained partly in terms of the cell-membrane being pierced by pores through which ions can move freely and partly in terms of highly concentrated cell ions, all of which are mobile.     

Halobacterium volcanii spec. nov., a Dead Sea halobacterium with a moderate salt requirement.

A halophilic bacterium was isolated from bottom sediment from the Dead Sea. The organism possessed the properties of the halobacteria, but differed from the known species in two important respects, 1) the cells were disc shaped and often cupped when grown under optimum conditions, 2) the optimum requirements for sodium chloride was in the range 1.7--2.5 molar which is about half of that generally reported for the halobacteria. The organism was assigned to the genus Halobacterium and described as Halobacterium volcanni spec. rov. The optimum sodium chloride concentration for growth was close to that found in the Dead Sea. The tolerance for magnesium chloride was very high; the organism grew well in media containing magnesium chloride in the concentrations found in the Dead Sea. Halobacterium volcanii is therefore remarkably well fitted for life in the Dead Sea.     

Halobacterium volcanii spec. nov., a Dead Sea halobacterium with a moderate salt requirement

A halophilic bacterium was isolated from bottom sediment from the Dead Sea. The organism possessed the properties of the halobacteria, but differed from the known species in two important respects, 1) the cells were disc-shaped and often cupped when grown under optimum conditions, 2) the optimum requirements for sodium chloride was in the range 1.7–2.5 molar which is about half of that generally reported for the halobacteria. The organism was assigned to the genus Halobacterium and described as Halobacterium volcanii spec.nov. The optimum sodium chloride concentration for growth was close to that found in the Dead Sea. The tolerance for magnesium chloride was very high; the organism grew well in media containing magnesium chloride in the concentrations found in the Dead Sea. Halobacterium volcanii is therefore remarkably well fitted for life in the Dead Sea.     

Haloarcula marismortui (Volcani) sp. nov., nom. rev., an extremely halophilic bacterium from the Dead Sea

An extremely halophilic red archaebacterium isolated from the Dead Sea (Ginzburg et al., J. Gen. Physiol. 55: 187-207, 1970) belongs to the genus Haloarcula and differs sufficiently from the previously described species of the genus to be designated a new species; we propose the name Haloarcula marismortui (Volcani) sp. nov., nom. rev. because of the close resemblance of this organism to "Halobacterium marismortui," which was first described by Volcani in 1940. The type strain is strain ATCC 43049.     

Distribution of non-electrolytes in Halobacterium cells. I. Halobacterium marismortui.

Halobacterium marismortui is an obligatorily halophilic species isolated from the Dead Sea. When inulin, fructose or glycerol are added to suspensions of bacteria, the amounts of these substances recovered from centrifuges pellets are more than could have been present in the extracellular space. Thus a certain amount becomes associated with the bacteria, though not enough to equilibrate with all the cell water. The inulin or fructose concentration found after uptake of these substances was correlated with the cell sodium concentration. It is argued that inulin, fructose or glycerol is unlikely to be adsorbed on the outside of the bacteria and more probably crosses the plasma membrane. A possible scheme for explaining the data is presented.     

Phylogenetic analyses of some extremely halophilic archaea isolated from Dead Sea water, determined on the basis of their 16S rRNA sequences.

Twenty-two extremely halophilic aerobic archaeal strains were isolated from enrichments prepared from Dead Sea water samples collected 57 years ago. The isolates were phenotypically clustered into five different groups, and a representative from each group was chosen for further study. Almost the entire sequences of the 16S rRNA genes of these representatives, and of Haloarcula hispanica ATCC 33960, were determined to establish their phylogenetic positions. The sequences of these strains were compared to previously published sequences of 27 reference halophilic archaea (members of the family Halobacteriaceae) and two other archaea, Methanobacterium formicicum DSM 1312 and Methanospirillum hungatei DSM 864. Phylogenetic analysis using approximately 1,400 base comparisons of 16S rRNA-encoding gene sequences demonstrated that the five isolates clustered closely to species belonging to three different genera--Haloferax, Halobacterium, and Haloarcula. Strains E1 and E8 were closely related and identified as members of the species Haloferax volcanii, and strain E12 was closely related and identified as a member of the species Halobacterium salinarum. However, strains E2 and E11 clustered in the Haloarcula branch with Haloarcula hispanica as the closest relative at 98.9 and 98.8% similarity, respectively. Strains E2 and E11 could represent two new species of the genus Haloarcula. However, because strains of these two new species were isolated from a single source, they will not be named until additional strains are isolated from other sources and fully characterized.     

Characterization of the dominant halophilic archaea in a bacterial bloom in the dead sea

Abstract A mass bloom of halophilic archaea developed in the Dead Sea in the summer of 1992, with peak densities of more than 3 × 10⁷ cells/ml, imparting a red coloration to the water. Microscopical examination showed a numerical dominance of pleomorphic, flat cells. Attempts to identify the dominant type of halophilic archaea by means of growth experiments, both on agar plates and by dilution in liquid media, were unsuccessful, as viable counts obtained were two or more orders of magnitude lower than the total microscopic counts. Analysis of the polar lipids in the Dead Sea biomass during the bloom showed one major glycolipid to be present in the extracts, corresponding with the sulfated diglycosyl diether lipid (S-DGD-1) characteristic of the genus Haloferax . No indications were found for the presence of significant amounts of other glycolipids that indicate the presence of large numbers of Dead Sea archaea such as Halobacterium sodomense or Haloarcula marismortui , or Halobacterium species such as H. halobium, H. salinarium and H. saccharovorum . Thus, the numerically dominant organisms in the bloom is probably a difficult to culture, not yet isolated, representative of the genus Haloferax .     

Taxonomic analysis of extremely halophilic archaea isolated from 56-years-old dead sea brine samples

A taxonomic study comprising both phenotypic and genotypic characterization, has been carried out on a total of 158 extremely halophilic aerobic archaeal strains. These strains were isolated from enrichments prepared from Dead Sea water samples dating from 1936 that were collected by B. E. Volcani for the demonstration of microbial life in the Dead Sea. The isolates were examined for 126 morphological, physiological, biochemical and nutritional tests. Numerical analysis of the data, by using the S(J) coefficient and UPGMA clustering method, showed that the isolates clustered into six phenons. Twenty-two out of the 158 strains used in this study were characterized previously (ARAHAL et al., 1996) and were placed into five phenotypic groups. The genotypic study included both the determination of the guanineplus-cytosine content of the DNA and DNA-DNA hybridization studies. For this purpose, representative strains from the six phenons were chosen. These groups were found to represent some members of three different genera - Haloarcula (phenons A, B, and C), Haloferax (phenons D and E) and Halobacterium (phenon F) - of the family Halobacteriaceae, some of them never reported to occur in the Dead Sea, such as Haloarcula hispanica, while Haloferax volcanii (phenons D and E) was described in the Dead Sea by studies carried out several decades later than Volcani's work.     

Transfer of Halobacterium denitrificans (Tomlinson, Jahnke, and Hochstein) to the genus Haloferax as Haloferax denitrificans comb. nov

Halobacterium denitrificans (Tomlinson, Jahnke, and Hochstein) was described at a time when the taxonomic subdivision of the family Halobacteriaceae was in a state of flux. On the basis of both biochemical and chemotaxonomic data, this organism exhibits features which indicate that it is more closely related to members of the genus Haloferax. On the basis of such criteria, we propose that Halobacterium denitrificans be reclassified as Haloferax denitrificans comb. nov. The type strain is strain ATCC 35960 (= DSM 4425).     

The ecology and taxonomy of anaerobic halophilic eubacteria

Abstract A number of obligately anaerobic chemoorganotrophic moderately halophilic bacteria have been isolated from the bottom sediments of the Dead Sea and the Great Salt Lake, Utah: (1) Halobacteroides halobius , a long motile rod from the Dead Sea, fermenting sugars to ethanol, acetate, H₂ and CO₂; (2) Clostridium lortetii , a rod-shaped bacterium from the Dead Sea, producing endospores with attached gas vacuoles; (3) a spore-forming motile rod-shaped bacterium, fermenting sugars, isolated from the Dead Sea; (4) Haloanaerobium praevalens , isolated from the Great Salt Lake, fermenting carbohydrates, peptides, amino acids and pectin to acetate, propionate, butyrate, H₂ and CO₂.
Analysis of their 16S rRNA shows that these organisms are related to each other, but unrelated to any of the other subgroups of the eubacterial kingdom, to which they belong.
Ha. praevalens and Hb. halobius regulate their internal osmotic pressure by the accumulation of salt (Na⁺, K⁺, Cl⁻) rather than by organic osmotic solutes.     

Comparison of purple membrane from Halobacterium cutirubrum and Halobacterium halabium.

Direct comparison of purple membrane preparations from Halobacterium cutirubrum and Halobacterium halobium was carried out. Both preparations were found to be essentially identical with respect to their molecular weight, retinal content, lipid composition, fingerprinting of peptides from peptide digestion, electron micrographs and X-ray diffraction patterns, and behaviour as a light-activated proton pump. Thus, there would appear to be no species differences in the purple membranes from these two bacteria.     

Survival of Filamentous Fungi in Hypersaline Dead Sea Water

A variety of filamentous fungi have recently been isolated from the Dead Sea (340 g/L total dissolved salts). To assess the extent to which such fungi can survive for prolonged periods in Dead Sea water, we examined the survival of both spores and mycelia in undiluted Dead Sea water and in Dead Sea water diluted to different degrees with distilled water. Mycelia of Aspergillus versicolor and Chaetomium globosum strains isolated from the Dead Sea remained viable for up to 8 weeks in undiluted Dead Sea water. Four Dead Sea isolates (A. versicolor, Eurotium herbariorum, Gymnascella marismortui, and C. globosum) retained their viability in Dead Sea water diluted to 80% during the 12 weeks of the experiment. Mycelia of all species survived for the full term of the experiment in Dead Sea water diluted to 50% and 10% of its original salinity. Comparison of the survival of Dead Sea species and closely related isolates obtained from other locations showed prolonged viability of the strains obtained from the Dead Sea. Spores of isolates obtained from the terrestrial shore of the Dead Sea generally proved less tolerant to suspension in undiluted Dead Sea water than spores of species isolated from the water column. Spores of the species isolated from the control sites had lost their viability in undiluted Dead Sea water within 12 weeks. However, with the exception of Emericella spores, which showed poor survival, a substantial fraction of the spores of Dead Sea fungal isolates remained viable for that period. The difference in survival rate between spores and mycelia of isolates of the same species points to the existence of adapted halotolerant and/or halophilic fungi in the Dead Sea.     

An alpha-like DNA polymerase from Halobacterium halobium

Two DNA polymerases have been isolated from extracts of Halobacterium halobium, one having a sedimentation coefficient of 11 S, designated as alpha-like polymerase and possessing the following characteristics. It is sensitive to both aphidicolin and N-ethylmaleimide but indifferent to the presence of a dideoxynucleoside triphosphate. Therefore this polymerase is very similar to the alpha DNA polymerase of eukaryotes. The enzyme requires 5 M NaCl for maximum activity. The other polymerase has a sedimentation coefficient of 4.4 S and is resistant to both aphidicolin and N-ethylmaleimide. However, it is inhibited by a dideoxynucleoside triphosphate.     

Halobacterium denitrificans sp. nov., an extremely halophilic denitrifying bacterium

Halobacterium denitrificans was one of several carbohydrate-utilizing, denitrifying, extremely halophilic bacteria isolated by anaerobic enrichment in the presence of nitrate. Anaerobic growth took place only when nitrate (or nitrite) was present and was accompanied by the production of dinitrogen. In the presence of high concentrations of nitrate (i.e., 0.5%), nitrous oxide and nitrite were also detected. When grown aerobically in a mineral-salts medium containing 0.005% yeast extract, H. denitrificans utilized a variety of carbohydrates as sources of carbon and energy. In every case, carbohydrate utilization was accompanied by acid production. A type culture has been deposited with the American Type Culture Collection, Rockville, Md. (ATCC 35960).     

Induction of a dissimilatory reduction pathway of nitrate in Halobacterium of the Dead Sea. A possible role for the 2 Fe-ferredoxin isolated from this organism

The processes involved in nitrate metabolism in Halobacterium of the Dead Sea are part of a dissimilatory pathway operating in these bacteria. The induction of both nitrate and nitrite reductases is shown to depend on the presence of nitrate and of anaerobic conditions. The gas products of the denitrification process were identified as nitrous oxide and nitrogen. Some properties of two of the enzymes involved in this process, nitrate and nitrite reductases, are reported. It is shown that the 2 Feferredoxin, which is present in large quantities in Halobacterium of the Dead Sea, can serve as an electron donor for nitrite reduction by nitrite reductase. It is suggested that the presence of a dissimilatory pathway for the reduction of nitrate in Halobacterium of the Dead Sea can be used as a tool for its classification.     

Microbial and chemical characterization of underwater fresh water springs in the Dead Sea

Due to its extreme salinity and high Mg concentration the Dead Sea is characterized by a very low density of cells most of which are Archaea. We discovered several underwater fresh to brackish water springs in the Dead Sea harboring dense microbial communities. We provide the first characterization of these communities, discuss their possible origin, hydrochemical environment, energetic resources and the putative biogeochemical pathways they are mediating. Pyrosequencing of the 16S rRNA gene and community fingerprinting methods showed that the spring community originates from the Dead Sea sediments and not from the aquifer. Furthermore, it suggested that there is a dense Archaeal community in the shoreline pore water of the lake. Sequences of bacterial sulfate reducers, nitrifiers iron oxidizers and iron reducers were identified as well. Analysis of white and green biofilms suggested that sulfide oxidation through chemolitotrophy and phototrophy is highly significant. Hyperspectral analysis showed a tight association between abundant green sulfur bacteria and cyanobacteria in the green biofilms. Together, our findings show that the Dead Sea floor harbors diverse microbial communities, part of which is not known from other hypersaline environments. Analysis of the water's chemistry shows evidence of microbial activity along the path and suggests that the springs supply nitrogen, phosphorus and organic matter to the microbial communities in the Dead Sea. The underwater springs are a newly recognized water source for the Dead Sea. Their input of microorganisms and nutrients needs to be considered in the assessment of possible impact of dilution events of the lake surface waters, such as those that will occur in the future due to the intended establishment of the Red Sea-Dead Sea water conduit.     

Microbiology Study of a Hypersaline Lake in French Somaliland

In a study of a lake having a higher concentration of salts than the Dead Sea, all of the heterotrophic bacteria isolated were aerobes; no strictly anaerobic strains were found. Ninety percent of the strains were euryhalines and ten percent were strict halophiles. The extreme halophiles belonged to the species Halobacterium trapanicum and Halococcus morrhuae.     

Polypeptide elongation factor Tu from Halobacterium marismortui

A GDP-binding protein of 60 kDa from Halobacterium marismortui has been purified to homogeneity. The purification has been carried out in high-salt buffers or in 50% glycerol buffers to protect the halophilic protein from denaturation. Evidence that this protein is the halophilic elongation factor Tu (hEF-Tu) is provided by the high homology of its N terminus with the corresponding sequences of other EF-Tus, and by immunological studies. Like some other EF-Tus the native protein can be cleaved with trypsin without concomitant loss of GDP-binding ability. The molecular mass of this hEF-Tu is higher than that for the corresponding factors from other sources including the halobacterium Halobacterium cutirubrum. The protein possesses typical halophilic characteristics, in that it is stable and active in 3 M KCl or 2 M (NH4)2SO4. Some other properties, like autofragmentation under sample treatment before SDS-PAGE, are described.