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At least 19 recordsLinked to original sources
PubMed1996

Time-domain reflectometry studies on Halobacterium halobium and Halobacterium marismortui.

The dielectric properties of Halobacterium halobium and Halobacterium marismortui measured over the frequency range 1 MHz to 1 GHz are compared with a single-shell model for interfacial polarization. In the case of Halobacterium halobium, the model shows excellent agreement with the experimental data for reasonable values of membrane and cytoplasmic conductivity and permittivity. For Halobacterium marismortui however, an acceptable fit to the data can only be achieved by invoking a plasma membrane conductivity some three orders of magnitude larger than that of Halobacterium halobium and adding a second high-frequency dielectric dispersion. These observations confirm the findings of a previous study and are consistent with a scheme for Halobacterium marismortui involving thermodynamic compartmentalization of Na and K ions and the existence of a conductive plasma membrane.

Cell Membrane↗
PubMed1978

Comparative studies on the fine structure of purple membrane from Halobacterium Cutirubrum and Halobacterium Halobium.

Direct comparison of the absorption and circular dichroic spectra of dark- and light-adapted purple membrane from Halobacterium cutirubrum and Halobacterium halobium indicated no apparent species differences. In addition, sequential bleaching and regeneration of the purple membrane with concomitant monitoring of the absorption and circular dichroic spectra showed no species differences as well. Furthermore, perturbation of the structure of the purple membrane from either species with a detergent, Triton X-100, yielded similar spectral changes. It was concluded: (i) no apparent differences exist in the molecular organization and protein fine structure of the two purple membranes, (ii) if exciton interaction among the retinal chromophores is a reasonable possibility in the case of the purple membrane from Halobacterium halobium, it must be similarly so for the membrane from Halobacterium cutirubrum, (iii) the effects of light adaptation on the membrane structure of both species are essentially the same, and (iv) the underlying molecular mechanisms for the bleaching and regenerative processes must be similar, if not identical, for the purple membranes of the two species.

Bacteriorhodopsins↗
PubMed1988

The taxonomic status of "Halobacterium marismortui" from the Dead Sea: a comparison with Halobacterium vallismortis.

A Halobacterium strain, isolated by Ginzburg et al. from the Dead Sea in the late 1960's, often referred to as "Halobacterium marismortui" or "Halobacterium of the Dead Sea" (deposited in the American Type Culture Collection as ATCC 43049) was compared with Halobacterium (Haloarcula) vallismortis ATCC 29715. The strains appeared to be very closely related, as shown by the near identity of their 5S and 16S ribosomal RNA's, and a large number of other common properties. Distinct differences exist, however, in cell morphology, and in their potency to utilize different sugars and other compounds.

Base Sequence↗
PubMed2004

Halobacterium noricense sp. nov., an archaeal isolate from a bore core of an alpine Permian salt deposit, classification of Halobacterium sp. NRC-1 as a strain of H. salinarum and emended description of H. salinarum.

Two rod-shaped haloarchaeal strains, A1 and A2, were isolated from a bore core from a salt mine in Austria. The deposition of the salt is thought to have occurred during the Permian period (225-280 million years ago). The 16S rDNA sequences of the strains were 97.1% similar to that of the type species of the genus Halobacterium, which was also determined in this work. Polar lipids consisted of C20-C20 derivatives of phosphatidylglycerol, methylated phosphatidylglycerol phosphate, phosphatidylglycerol sulfate, triglycosyl diether and sulfated tetraglycosyl diether. Optimal salinity for growth was 15-17.5% NaCl; Mg++ was tolerated up to a concentration of 1 M. The DNA-DNA reassociation value of strain A1T was 25% with H. salinarum DSM 3754T and 41% with Halobacterium sp. NRC-1, respectively. Based on these results and other properties, e.g. whole cell protein patterns, menaquinone content and restriction patterns of DNA, strains A1 and A2 are members of a single species, for which we propose the name H. noricense. The type strain is A1 (DSM 15987T, ATCC BAA-852T, NCIMB 13967T). Since we present evidence that Halobacterium sp. NRC-1 is a member of H. salinarum, an emended description of H. salinarum is provided.

Archaeal Proteins↗
PubMed1996

The repair of ultraviolet light-induced DNA damage in the halophilic archaebacteria, Halobacterium cutirubrum, Halobacterium halobium and Haloferax volcanii.

Extremely halophilic archaebacteria have been reported to have no capacity for dark repair (excision repair) of ultraviolet damage and to rely on very efficient photoreactivation for recovery after UVC irradiation. Post-UV incubation in the light restores 100% survival in these organisms. This has been taken to indicate that cyclobutane dimers are the only significant UV-induced lesions and that they are completely repaired by photoreactivation. However, in all organisms studied to date, pyrimidine (6-4) pyrimidone photoproducts are a significant cytotoxic and mutagenic lesion and constitute 10-30% of UV photoproducts. The question arises, therefore--are 6-4 photoproducts induced in the halophilic archaebacteria and, if they are, how are they repaired? This paper shows that both cyclobutane dimers and 6-4 photoproducts are induced in the extremely halophilic archaebacteria, Halobacterium cutirubrum, Halobacterium halobium and Haloferax volcanii, at similar levels as in other organisms. Furthermore, contrary to previous reports, there is dark repair of both lesions. As in other organisms, 6-4 photoproducts are removed more efficiently than cyclobutane dimers in the dark. In the light, cyclobutane dimers are repaired very rapidly and there is also photoenhanced repair of 6-4 photoproducts. This work confirms that organisms such as Halobacterium and Haloferax which live in conditions of high exposure to sunlight have very efficient rates of repair of UV lesions in the light.

DNA Damage↗
PubMed1975

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.

Amino Acids↗
PubMed1976

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.

Bacteriorhodopsins↗
PubMed1996

Fermentative arginine degradation in Halobacterium salinarium (formerly Halobacterium halobium): genes, gene products, and transcripts of the arcRACB gene cluster.

Fermentative growth via the arginine deiminase pathway is mediated by the enzymes arginine deiminase, carbamate kinase, and catabolic ornithine transcarbamylase and by a membrane-bound arginine-ornithine antiporter. Recently we reported the characterization of catabolic ornithine transcarbamylase and the corresponding gene, arcB, from Halobacterium salinarium (formerly Halobacterium halobium). Upstream of the arcB gene, three additional open reading frames with halobacterial codon usage were found. They were identified as the arcC gene coding for carbamate kinase, the arcA gene coding for arginine deiminase, and a gene, tentatively termed arcR, coding for a putative regulatory protein. The identification of the arcC and arcA genes was verified, respectively, by heterologous expression of the enzyme in Haloferax volcanii and by protein isolation and N-terminal sequence determination of three peptides. The gene order arcRACB differs from the gene order arcDABC in Pseudomonas aeruginosa, the only other organism for which sequence information is available. Transcripts from H. salinarium cultures grown fermentatively or aerobically were characterized by Northern (RNA) blot and primer extension analyses. It was determined (i) that monocistronic transcripts corresponding to the four open reading frames exist and that there are three polycistronic transcripts, (ii) that the level of induction during fermentative growth differs for the various transcripts, and (iii) that upstream of the putative transcriptional start sites for the three structural genes there are sequences with similarities to the halobacterial consensus promoter. The data indicate that expression of the arc gene cluster and its regulation differ in H. salinarium and P. aeruginosa.

Amino Acid Sequence↗
PubMed1989

The expression of the superoxide dismutase gene in Halobacterium cutirubrum and Halobacterium volcanii.

The gene encoding the Mn-containing superoxide dismutase (SOD) from Halobacterium cutirubrum has been cloned and sequenced. The deduced amino acid sequence is homologous to the sequences of Fe and Mn SODs from eubacteria. The high degree of amino acid identity between the archaebacterial and eubacterial proteins suggests that a SOD gene may have been laterally transferred between eubacteria and archaebacteria sometime after the accumulation of atmospheric oxygen. Consensus elements of halobacterial promoters are found upstream of the coding region, however, the spacing between them and the transcription start site is greater than in other genes. Termination of transcription occurs in five consecutive T residues that are preceded by a GC-rich sequence that has short inverted repeats. In addition to the authentic SOD gene, H. cutirubrum also contains a putative pseudogene. The SOD levels and growth rates of H. cutirubrum and Halobacterium volcanii were tested in response to treatment by paraquat, an intracellular generator of superoxide. In H. volcanii the growth rate slowed, and SOD was strongly induced throughout prolonged treatment with paraquat. In H. cutirubrum the same effects were noticed initially, but after 48 h exposure to the drug, the growth rate increased and the SOD level decreased. Production of paraquat resistant mutants of H. cutirubrum may play a part in this process, however, some type of physiological adaptation is also probably required.

Amino Acid Sequence↗
PubMed1979

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.

Cell Membrane Permeability↗
PubMed1988

The cell wall structure of a magnesium-dependent halobacterium, Halobacterium volcanii CD-2, from the Dead Sea.

Cell wall preparations from the magnesium-dependent halophilic bacterium, Halobacterium volcanii, were studied by high-resolution electron microscopy complemented with image analysis and processing. For ultrastructural studies, specimens were prepared by a variety of methods, including negative staining, and metal shadowing after air-drying, freeze-drying, or freeze-fracturing and etching. All methods revealed the cell wall to be composed of a near-hexagonal lattice of unit cells having a center-to-center spacing of 15.5 nm. While negatively stained samples yielded two types variably revealed the unit cell to be composed of six protomers surrounding a central mass depression. This low-resolution unit cell morphology appears very similar to that of other bacterial cell wall S-layers studied to date.

Cell Wall↗
PubMed2005

Physiological responses of the halophilic archaeon Halobacterium sp. strain NRC1 to desiccation and gamma irradiation.

We report that the halophilic archaeon Halobacterium sp. strain NRC-1 is highly resistant to desiccation, high vacuum and 60Co gamma irradiation. Halobacterium sp. was able to repair extensive double strand DNA breaks (DSBs) in its genomic DNA, produced both by desiccation and by gamma irradiation, within hours of damage induction. We propose that resistance to high vacuum and 60Co gamma irradiation is a consequence of its adaptation to desiccating conditions. Gamma resistance in Halobacterium sp. was dependent on growth stage with cultures in earlier stages exhibiting higher resistance. Membrane pigments, specifically bacterioruberin, offered protection against cellular damages induced by high doses (5 kGy) of gamma irradiation. High-salt conditions were found to create a protective environment against gamma irradiation in vivo by comparing the amount of DSBs induced by ionizing radiation in the chromosomal DNA of Halobacterium sp. to that of the more radiation-sensitive Escherichia coli that grows in lower-salt conditions. No inducible response was observed after exposing Halobacterium sp. to a nonlethal dose (0.5 kGy) of gamma ray and subsequently exposing the cells to either a high dose (5 kGy) of gamma ray or desiccating conditions. We find that the hypersaline environment in which Halobacterium sp. flourishes is a fundamental factor for its resistance to desiccation, damaging radiation and high vacuum.

Cobalt Radioisotopes↗
PubMed2006

Proteomic analysis of acidic chaperones, and stress proteins in extreme halophile Halobacterium NRC-1: a comparative proteomic approach to study heat shock response.

BACKGROUND: Halobacterium sp. NRC-1 is an extremely halophilic archaeon and has adapted to optimal growth under conditions of extremely high salinity. Its proteome is highly acidic with a median pI of 4.9, a unique characteristic which helps the organism to adapt high saline environment. In the natural growth environment, Halobacterium NRC-1 encounters a number of stressful conditions including high temperature and intense solar radiation, oxidative and cold stress. Heat shock proteins and chaperones play indispensable roles in an organism's survival under many stress conditions. The aim of this study was to develop an improved method of 2-D gel electrophoresis with enhanced resolution of the acidic proteome, and to identify proteins with diverse cellular functions using in-gel digestion and LC-MS/MS and MALDI-TOF approach. RESULTS: A modified 2-D gel electrophoretic procedure, employing IPG strips in the range of pH 3-6, enabled improved separation of acidic proteins relative to previous techniques. Combining experimental data from 2-D gel electrophoresis with available genomic information, allowed the identification of at least 30 cellular proteins involved in many cellular functions: stress response and protein folding (CctB, PpiA, DpsA, and MsrA), DNA replication and repair (DNA polymerase A alpha subunit, Orc4/CDC6, and UvrC), transcriptional regulation (Trh5 and ElfA), translation (ribosomal proteins Rps27ae and Rphs6 of the 30 S ribosomal subunit; Rpl31eand Rpl18e of the 50 S ribosomal subunit), transport (YufN), chemotaxis (CheC2), and housekeeping (ThiC, ThiD, FumC, ImD2, GapB, TpiA, and PurE). In addition, four gene products with undetermined function were also identified: Vng1807H, Vng0683C, Vng1300H, and Vng6254. To study the heat shock response of Halobacterium NRC-1, growth conditions for heat shock were determined and the proteomic profiles under normal (42 degrees C), and heat shock (49 degrees C) conditions, were compared. Using a differential proteomic approach in combination with available genomic information, bioinformatic analysis revealed five putative heat shock proteins that were upregulated in cells subjected to heat stress at 49 degrees C, namely DnaJ, GrpE, sHsp-1, Hsp-5 and sHsp-2. CONCLUSION: The modified 2-D gel electrophoresis markedly enhanced the resolution of the extremely acidic proteome of Halobacterium NRC-1. Constitutive expression of stress proteins and chaperones help the organism to adapt and survive under extreme salinity and other stress conditions. The upregulated expression pattern of putative chaperones DnaJ, GrpE, sHsp-1, Hsp-5 and sHsp-2 under elevated temperature clearly suggests that Halobacterium NRC-1 has a sophisticated defense mechanism to survive in extreme environments.

Journal Article↗
PubMed2006

The uvrA, uvrB and uvrC genes are required for repair of ultraviolet light induced DNA photoproducts in Halobacterium sp. NRC-1.

BACKGROUND: Sequenced archaeal genomes contain a variety of bacterial and eukaryotic DNA repair gene homologs, but relatively little is known about how these microorganisms actually perform DNA repair. At least some archaea, including the extreme halophile Halobacterium sp. NRC-1, are able to repair ultraviolet light (UV) induced DNA damage in the absence of light-dependent photoreactivation but this 'dark' repair capacity remains largely uncharacterized. Halobacterium sp. NRC-1 possesses homologs of the bacterial uvrA, uvrB, and uvrC nucleotide excision repair genes as well as several eukaryotic repair genes and it has been thought that multiple DNA repair pathways may account for the high UV resistance and dark repair capacity of this model halophilic archaeon. We have carried out a functional analysis, measuring repair capability in uvrA, uvrB and uvrC deletion mutants. RESULTS: Deletion mutants lacking functional uvrA, uvrB or uvrC genes, including a uvrA uvrC double mutant, are hypersensitive to UV and are unable to remove cyclobutane pyrimidine dimers or 6-4 photoproducts from their DNA after irradiation with 150 J/m2 of 254 nm UV-C. The UV sensitivity of the uvr mutants is greatly attenuated following incubation under visible light, emphasizing that photoreactivation is highly efficient in this organism. Phylogenetic analysis of the Halobacterium uvr genes indicates a complex ancestry. CONCLUSION: Our results demonstrate that homologs of the bacterial nucleotide excision repair genes uvrA, uvrB, and uvrC are required for the removal of UV damage in the absence of photoreactivating light in Halobacterium sp. NRC-1. Deletion of these genes renders cells hypersensitive to UV and abolishes their ability to remove cyclobutane pyrimidine dimers and 6-4 photoproducts in the absence of photoreactivating light. In spite of this inability to repair UV damaged DNA, uvrA, uvrB and uvrC deletion mutants are substantially less UV sensitive than excision repair mutants of E. coli or yeast. This may be due to efficient damage tolerance mechanisms such as recombinational lesion bypass, bypass DNA polymerase(s) and the existence of multiple genomes in Halobacterium. Phylogenetic analysis provides no clear evidence for lateral transfer of these genes from bacteria to archaea.

Journal Article↗
PubMed1978

Passive electrical properties of Halobacterium species. I. Low-frequency range.

The electrical conductivity of suspensions of two species of Halobacterium was measured at low A. C. frequency. The results obtained from Halobacterium 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.

Cell Count↗
PubMed2002

Purification and characterization of an extremely halophilic acetoacetyl-CoA thiolase from a newly isolated Halobacterium strain ZP-6.

The extremely halophilic archaeon ZP-6 was isolated from Ai-Ding salt lake in Xinjiang Uighur Autonomous Region of the People's Republic of China. Based on its physiological properties, 16S rDNA sequence, and DNA-DNA homology with known haloarchaea, the isolate was tentatively identified as a Halobacterium sp. An acetoacetyl-CoA thiolase was purified and characterized from this organism. The native enzyme has a molecular mass of 80 +/- 8 kDa and consists of two identical subunits of 43 +/- 2 kDa each. The N-terminus 14 amino acid residues were sequenced and showed identity with the respective part of a putative thiolase (AcaB1) of Halobacterium sp. NRC-1. The purified enzyme has an optimal pH of 7.9 for acetoacetyl-CoA thiolysis. The thiolytic activity was inhibited by the presence of Mg'- and was stimulated by KCl or NaCl. The thiolysis reaction of Halobacterium sp. ZP-6 thiolase can be inhibited by either substrate when present in excess. The distinct kinetic profile indicates that the thiolase from Halobacterium sp. ZP-6 may have a different catalytic mechanism from the so-called ping-pong mechanism employed by other thiolases. To our knowledge, this is the first report of the purification and characterization of a halophilic thiolase from an archaeal species.

Acetyl-CoA C-Acetyltransferase↗
PubMed2003

Repair of UV damage in Halobacterium salinarum.

Halobacterium is one of the few known Archaea that tolerates high levels of sunlight in its natural environment. Photoreactivation is probably its most important strategy for surviving UV irradiation and we have shown that both of the major UV photoproducts, cyclobutane pyrimidine dimers (CPDs) and (6-4) photoproducts, can be very efficiently repaired by photoreactivation in this organism. There are two putative photolyase gene homologues in the published genome sequence of Halobacterium sp. NRC-1. We have made a mutant deleted in one of these, phr2, and confirmed that this gene codes for a CPD photolyase. (6-4) photoproducts are still photoreactivated in the mutant so we are currently establishing whether the other homologue, phr1, codes for a (6-4) photolyase. We have also demonstrated an excision repair capacity that operates in the absence of visible light but the nature of this pathway is not yet known. There is probably a bacteria-type excision-repair mechanism, since homologues of uvrA, uvrB, uvrC and uvrD have been identified in the Halobacterium genome. However, there are also homologues of eukaryotic nucleotide-excision-repair genes ( Saccharomyces cerevisiae RAD3, RAD25 and RAD2 ) so there may be multiple repair mechanisms for UV damage in Halobacterium.

Animals↗