Halobacterium Species Research Articles

Characterization of the ribosomal RNA gene clusters in Halobacterium cutirubrum.

We present a comprehensive and detailed analysis of the structure and organization of a cloned ribosomal RNA gene cluster from the archaebacterial species Halobacterium cutirubrum. With the exception of a region in the middle of the 23 S rRNA gene, the DNA sequence of the entire gene cluster has been determined. The gene organization is similar to that found in typical eubacteria with the 16, 23, and 5 S genes occupying the proximal, middle, and distal positions, respectively. There appears to be no equivalent to the eucaryotic 5.8 S gene in H. cutirubrum. The cluster also contains two putative tRNA genes, an alanine tRNA gene in the 16-23 S intergenic space, and a cysteine tRNA gene distal to the 5 S rRNA gene. The 16 and 23 S rRNA genes are surrounded by long nearly perfect inverted repeat sequences which are presumably utilized along with other structural features of the RNA for the processing of 16 and 23 S rRNA from a large precursor transcript. The 5' sequence flanking the 16 S rRNA gene contains two imperfect copies, followed by three perfect copies of a bipartite direct-repeat unit. The sequence AAGTAA, believed to be an important component of the Halobacterium promotor, is present in the highly conserved portion of the direct repeat unit. In the 3' region flanking the 5 S rRNA gene there are sequences, a short inverted repeat followed by T5, and a G/C-rich region followed by an A/T-rich region, which may function in transcription termination. Genomic southern hybridization experiments clearly indicate that the ribosomal RNA genes are unique single-copy DNA in H. cutirubrum.

Homology of Gas Vesicle Proteins in Cyanobacteria and Halobacteria

Continuous N-terminal amino acid sequences between 26 and 64 residues long were determined for the gas vesicle protein (GVP) isolated from four genera of cyanobacteria and two species of halobacteria. Definite homology was established between the GVPsof all six organisms. Within the cyanobacteria the homologies varied from 98% to 85% with the order of decreasing similarity to Anabaena being Aphanizomenon, Oscillatoria, and Dactylococcopsis, in agreement with phylogenetic affinities. (Further homologies were also established between sequences at the C-terminus of GVP from Anabaena and Microcystis.) In the GVP from Halobacterium there was a short non-homologous sequence near the N-terminus followed by 39 residues showing 70% homology with GVP from Anabaena, and 79% with that from the halophilic Dactylo-coccopsis. An antibody raised against the Anabaena gas vesicles was effective in agglutinating gas vesicles from five different cyanobacteria, Microcyclus (a colourless eubacterium), the two halobacteria and Methanosarcina (another archaebacterium). The origin of the gas vesicle is discussed.

Dihydrolipoamide dehydrogenase from halophilic archaebacteria.

Dihydrolipoamide dehydrogenase has been discovered in the halophilic archaebacteria for the first time. The enzyme from both classical and alkaliphilic halobacteria has been investigated. (1) The enzyme specifically catalysed the stoichiometric oxidation of dihydrolipoamide by NAD+. Enzymic activity was optimal at 2 M-NaCl and was remarkably resistant to thermal denaturation. (2) The relative molecular masses (Mr) of the native enzyme from the various species of halobacteria were determined to be within the range 112000-120000. (3) The enzyme exhibited a hyperbolic dependence of catalytic activity on both dihydrolipoamide and NAD+ concentrations. From these steady-state kinetic measurements the dissociation constant (Ks) of dihydrolipoamide was determined to be 57 (+/- 5) microM. (4) The enzyme was only susceptible to inactivation by iodoacetic acid in the presence of its reducing ligands, dihydrolipoamide or NADH. The rate of inactivation followed a hyperbolic dependence on the concentration of dihydrolipoamide, from which the Ks of this substrate was calculated to be 55 (+/- 7) microM. Together with the steady-state kinetic data, the pattern of inactivations is consistent with the involvement in catalysis of a reversibly reducible disulphide bond, as has been found in dihydrolipoamide dehydrogenase from non-archaebacterial species. In eubacterial and eukaryotic organisms, dihydrolipoamide dehydrogenase functions in the 2-oxo acid dehydrogenase complexes. These multienzyme systems have not been detected in the archaebacteria, and, in the context of this apparent absence, the possible function and evolutionary significance of archaebacterial dihydrolipoamide dehydrogenase are discussed.

The sensitivity of halobacteria to antibiotics

Eleven species of the genera Halobacterium, Halococcus and the recently proposed Haloarcula were tested by the macro-broth dilution method for their sensitivity to 20 antibiotics with different modes of action. The most active were bacitracin, erythromycin, haloquinone, rifampicin and novobiocin. Resistant mutants of H. mediterranei to bacitracin, chloramphenicol and josamycin were obtained with frequencies of spontaneous mutation between 10−4 and 10−7.

The sensitivity of halobacteria to antibiotics

Eleven species of the genera Halobacterium, Halococcus and the recently proposed Haloarcula were tested by the macro-broth dilution method for their sensitivity to 20 antibiotics with different modes of action. The most active were bacitracin, erythromycin, haloquinone, rifampicin and novobiocin. Resistant mutants of H. mediterranei to bacitracin, chloramphenicol and josamycin were obtained with frequencies of spontaneous mutation between 10−4 and 10−7.

Halobacterium mediterranei spec, nov., a New Carbohydrate-Utilizing Extreme Halophile

The extremely halophilic rod-shaped bacterium, strain R-4, has features very different from other known Halobacterium species. As do all other extreme halophiles, the organism possesses a high excess of acidic over basic amino acids in its proteins, a cell wall lacking peptidoglycan, and ether-linked diphytanyl lipids. It differs from the "classic" halobacteria in several important ways: it can use many different compounds as sole sources of carbon and energy. It is strongly amylolytic and lipolytic (against different Tweens), and does not produce H(2)S. The cell envelope of R-4 is much thicker than that of other halobacteria. The proportions of polar lipids in the envelope are different, and a new glycolipid sulfate is present in this strain. The envelope has a relatively low protein content, although a glycoprotein similar to the one of Halobacterium salinarium was detected. The G + C content (60%) is lower than that of other halobacteria. It is suggested that R-4 be designated a new species, Halobacterium mediterranei.

Acetylene as an Inhibitor of Methanogenic Bacteria

Growth of six pure cultures of methanogens was inhibited by low concentrations of dissolved acetylene (C2H2); other archaebacteria (three Halobacterium species) and several eubacteria were not similarly affected. The minimum concentration of dissolved C2H2 required to inhibit growth of Methanospirillum hungatei completely was about 8 mu;m; dissolved ethylene at 20 μm had little effect on growth. Dissolved acetylene (33 mu;m) did not alter the E h of the medium, or result in a loss in viability of M. hungatei after 16 h exposures. In anaerobic cell extracts of M. hungatei, activities of hydrogenase, NADP reductase, methyl-coenzyme M reductase and ATP hydrolase were not inhibited by C2H2 concentrations several times higher than those required for growth inhibition. The intracellular ATP content of all of the methanogens dropped dramatically on exposure to C2H2. Moreover, cells of M. hungatei and Methanobacterium bryantii on exposure to C2H2 lost their ability to maintain a transmembrane pH gradient. We suggest that exposure to C2H2 results in a decline in methanogen functions which require a H+-flux, including ATP synthesis, Ni2+ uptake and methanogenesis.

Halobacterium pharaonis sp. nov., a New, Extremely Haloalkaliphilic Archaebacterium with Low Magnesium Requirement

Halobacterium pharaonis sp. nov. was isolated from the alkaline brines of eutrophic desert lakes of Wadi Natrun, Egypt. The new species differs from the Halobacterium species so far described in being alkaliphilic, in its extremely low Mg2+ requirement for growth, and in its DNA base composition (64.3 mol% guanine + cytosine, determined by thermal decomposition; no satellite DNA). Magnesium in concentrations above 0.01 mol/1 (≈ 0.25% w/v MgSO4·7H2O) inhibits growth. Good growth occurs between pH 7.7 and 9.3, optimal growth at pH 8.5.

Bacterial Photosynthesis without Chlorophyll

Research Article| May 01 1982 Bacterial Photosynthesis without Chlorophyll David Bardell David Bardell Search for other works by this author on: This Site PubMed Google Scholar The American Biology Teacher (1982) 44 (5): 278–313. https://doi.org/10.2307/4447503 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Cite Icon Cite Search Site Citation David Bardell; Bacterial Photosynthesis without Chlorophyll. The American Biology Teacher 1 May 1982; 44 (5): 278–313. doi: https://doi.org/10.2307/4447503 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentThe American Biology Teacher Search This content is only available via PDF. Copyright 1981 The National Association of Biology Teachers Article PDF first page preview Close Modal You do not currently have access to this content.

Characterization of plasmids in halobacteria.

Extrachromosomal, covalently closed circular deoxyribonucleic acid has been isolated from different species of halobacteria. Three strains of Halobacterium halobium and one of Halobacterium cutirubrum, all of which synthesize purple membrane (Pum+) and bacterioruberin (Rub+), contain plasmids of different size which share extensive sequence homologies. One strain of Halobacterium salinarium, another one of Halobacterium capanicum, and two new Halobacterium isolates from Tunisia, which are also Pum+ Rub+, do not harbor covalently closed circular deoxyribonucleic acid but contain sequences, presumably integrated into the chromosome, which are similar if not identical to those of pHH1, i.e., the plasmid originally isolated from H. halobium. Three other halophilic strains, Halobacterium trapanicum, Halobacterium volcanii, and a new isolate from Israel, do not carry pHH1-like sequences. These strains are, by morphological and physiological criteria, different from the others examined and harbor plasmids unrelated to pHH1.

An Alkalophilic Red Halophilic Bacterium with a Low Magnesium Requirement from a Kenyan Soda Lake

Summary: A Halobacterium species isolated from solar evaporation ponds and sodium sesquicarbonate deposits at Lake Magadi, Kenya, differs from known species of Halobacterium in its GC content, in being obligately alkalophilic with a pH optimum between 9.0 and 10.0, and in having a Mg2+ requirement of between 0.1 and 2.0 mm for optimum growth.

Halobacterium vallismortis sp. nov. An amylolytic and carbohydrate-metabolizing, extremely halophilic bacterium.

The extremely halophilic bacterium (formerly designated as strain J.F. 54) isolated from salt pools of the Death Valley, California, is a motile, Gram-negative, extremely pleomorphic organism, aerobe, and facultative anaerobe. A variety of carbohydrates are assimilated with or without acid production; soluble starch is hydrolyzed. The organism is not proteolytic; catalase, oxidase, and DNase reactions are positive; Tween 20 is slightly hydrolyzed, but Tweens 40, 60, and 80 are not. Nitrates are reduced to nitrites with gas production; nitrites are not reduced. Optimum growth temperature is 40 degrees C. Growth is inhibited by bacitracin and by novobiocin. The type strain J.F. 54 differs from described species of the genus Halobacterium and is assigned to a new species, Halobacterium vallismortis sp. nov.

Halobacterium strain 5 contains a plasmid which is correlated with the presence of gas vacuoles.

GAS vacuoles are subcellular inclusions in certain prokaryotic organisms which enclose a gas-filled space and consist of a proteinaceous membrane containing one or two very hydrophobic protein subunits1. Gas vacuoles are, with few exceptions, limited to aquatic microorganisms2, where it has been proposed either that they may be involved in regulating buoyancy, or that the light-scattering properties of the inclusions may protect the cells from the deleterious effects of high light intensities1. Several species of Halobacterium possess gas vacuoles3, and in certain strains, forms which lack gas vacuoles arise at a relatively high frequency. The rate of loss of gas vacuoles in Halobacterium strain 5 occurs so often that regular recloning of individual colonies containing gas vacuoles is necessary to maintain the wild-type strain4. Gas vacuoles are also lost spontaneously in other aquatic microorganisms, and it was this observation which led Walsby to propose that the gas-vacuole protein might be carried on a plasmid5. Plasmids have not previously been shown to exist in Halobacterium. All the obligate halophiles as yet examined contain a satellite DNA which may account for between 11 % and 36% of the total DNA (ref. 6, 7). Moore and McCarthy7, however, argued that the satellite DNA is not composed of multiple copies of a plasmid because its amount is unchanged by growing the cells in the presence of known plasmid-curing agents, and because total Halobacterium DNA renatures at a rate expected for single-copy DNA. Here I show that the wild-type Halobacterium strain 5 contains three plasmids, and also show a correlation between the presence of a plasmid of molecular weight (MW) 44×106 and the presence of gas vacuoles.

Regulation of cell volume and ion concentrations in a Halobacterium.

Changes in cell volume and ion content of a Halobacterium species are described in terms of the NaCl concentration (0.5--3.5M) and pH(4-8) of the suspending medium. Cell volume, per unit content of protein of bacteria in stationary phase cultures, rose as the [NaCl] of the growth medium was increased. Logarithmic-phase bacteria shrank as the pH fell from 7 to 5.5. These changes are characteristic of bacteria with a moderate or rapid rate of O2 consumption. Starving (i.e. nonmetabolizing) bacteria, on the other hand, did not change in size within the above ranges of [NaCl] and pH. At lower values, however, such bacteria swelled and eventually lysed. Effects of low pH on cell ions are compared in metabolizing and starving bacteria, and it is shown that changes in the state of the cell K are correlated with movements of cell Na. It appears that the cell K is used to maintain cell [Na] below the NaCl concentration of the medium. The results are explained in terms of a model involving interactions between polyelectrolytes, salts and water in the concentrated cytoplasm of these halophilic organisms.

Potash guar gum--a source of halophilic bacteria.

Moderate and extreme halophilic microorganisms have been isolated from guar gum solutions dissolved in potash brine for use in sylvite froth flotation. Tentative identifications have been made of vibrio, Halobacterium, and Halococcus species. Reinoculation of these isolates into guar gum solutions has shown that they are not carbohydrate-utilizing strains, but instead metabolize the contaminating proteins present in guar.

Bacitracin induces sphere formation in Halobacterium species which lack a wall peptidoglycan.

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Ultrastructure of two species of halobacterium

The morphology of a halobacterium from the Dead Sea has been compared with Halobacterium halobium. A freeze-fracture study has revealed two hexagonal patterns with repeating distances of 155 A and 65 A within layers of the cell-envelope. The larger pattern is a characteristic of the genus Halobacterium. The smaller has been identified with a surface of the cell-membrane. By the same freeze-fracture technique, the membrane adjacent to the cell-envelope was shown to be characterized by two particulate fracture faces, presumably within the hydrophobic region of the membrane. The Dead Sea Halobacterium was shown to contain poly-β-hydroxybutyric acid (PHB). Freeze-fractured cells contained granules similar to PHB granules found in other bacterial species. Alterations in the physiological state of the Dead Sea Halobacterium were found to have little effect on cell structure which was also unaffected by depletion of cell K.

Ion metabolism in a Halobacterium. I. Influence of age of culture on intracellular concentrations.

Work is described on the changes in cell ions during growth of cultures of a species of Halobacterium isolated from the Dead Sea. Cell K concentration fell from 5.5 to 3.8 moles per kg cell water during the logarithmic phase of growth and maintained the latter value during the stationary phase (initial medium concentration, 7 mM). Cell Na and Cl followed a complex series of roughly parallel changes. The logarithmic phase ion concentrations were: Na, 1.0-2.3 moles/kg cell water; Cl, 2.3-3.7 moles/kg cell water. The final stationary phase values were: Na, 0.5 moles/kg cell water; Cl, 2.3-2.9 moles/kg cell water (medium NaCl concentration, 3.9 Molal). It is suggested that most of the K(+) is bound within the cytoplasm.

The unusual membrane permeability of two halophilic unicellular organisms

1. 1. The permeability of a Halobacterium species and Dunaliella parva to several radioactive substances has been measured. 2. 2. The method used was to centrifuge a cell suspension, within which was dissolved the given radioactive substance, and measure the radioactivity of the resultant cell pellet and supernatant. The volume of radioactive substance within the cell pellet was then calculated. 3. 3. Both organisms were found to be impermeable to [ 14C]dextran (mol. wt. 80 000). 4. 4. Results indicated that the Halobacterium cell was freely permeable to [ 14C]-sucrose, [ 14C]inulin, [ 14C]starch, and even [ 14C]polyvinylpyrollidone (mol. Wt. 30 000–40 000). 5. 5. A region of the D. parva cell was permeable to [ 14C]surcose and to [ 14C]inulin. 6. 6. It is argued that the results indicate the existence of large pores in the cell membranes of these two organisms.

A study of the cell envelope of the halobacteria.

SUMMARY: Electron microscopy on thin sections of three different extremely halophilic Halobacterium species showed that their cell envelopes were of similar general construction: an inner membrane and an outer layer. The outer layer stains most strongly in the outermost part. When the NaCl concentration of the environment was lowered from the optimal of 4·3 m to 2·2 m the outer layer of the cell envelope of Halobacterium salinarium strain 1 became frayed; in many cells a release of material from the outer layer appeared to take place. When the cells were exposed to distilled water the outer layer of the envelope appeared to dissolve completely and the cell membrane disintegrated into tiny flakes. Fragments of the cell envelope produced by mechanical disintegration of the cells in 4·3 m-NaCl formed closed vesicles very rapidly; some of the cytoplasmic material became trapped inside the vesicles. Detergents appeared to slow down the closing of the vesicles and also to cause a release of material from the outer layer of the cell envelope. The cell envelope vesicles were mainly composed of protein and lipid; their content of amino sugar was low compared with the cell envelope of other Gram-negative bacteria. The cell envelope vesicle also contained nucleic acids; most of these were probably parts of the cytoplasmic material trapped inside the vesicles. The amino acid composition showed that the protein of the cell envelope vesicles was quite acidic, consistent with the contention that high concentrations of sodium ions stabilize the cell envelopes of these organisms by neutralizing the negative charges of the protein. Upon centrifugation at high speed of the lysate obtained by dialysis of the cell envelope vesicles against distilled water, the fragments of the cell membrane sedimented whereas most of the protein, presumably from the outer layer of the cell envelope, stayed in the supernatant fraction. Carotenoids and cytochromes were contained in the sediment with the membrane fragments. Most of the amino sugar-containing components stayed in the supernatant fraction; in the presence of 10–25 m salt most of the amino sugar-containing components sediment with the membrane fragments.