Disclinations

Harris, W. F.

doi:10.1038/scientificamerican1277-130

Cited by 88 publications

(53 citation statements)

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“…As opposed to the extracellular surface, the cytoplasmic surface of the S-layer only bound PCF in a random, dense layer (not shown). Dislocations, as observed in many S-layers (8,22,23), could not be found in the cylindrical regions of the sacculi.…”

Section: Resultsmentioning

confidence: 93%

Ultrastructure of the cell envelope of the archaebacteria Thermoproteus tenax and Thermoproteus neutrophilus

Messner¹,

Pum²,

Sára³

et al. 1986

J Bacteriol

141

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The ultrastructures of the regular surface layers (S-layers) of the extremely thermophilic archaebacteria Thermoproteus tenax and Thermoproteus neutrophilus were examined by freeze-etching, freeze-drying, and negative staining methods combined with optical and digital image enhancement. In both strains, a monolayer of macromolecules arranged in hexagonal arrays with center-to-center spacings of approximately 30 nm was the only component of the cell wall. The gross morphologies of the S-layer lattices of the two organisms were similar and showed the same handedness in the arrangement of the protomers of the morphological units. Striking differences were found in the anionic charge distributions on the surfaces of the two S-layer proteins as determined by labeling with polycationic ferritin. Analysis of the lattice orientation, together with the number and distribution of lattice faults on intact cells, provided a strong indication that the S-layers of both organisms have a shape-determining function.Thermoproteus tenax (29) and Thermoproteus neutrophilus (6) are members of a recently discovered, novel order of extremely thermophilic anaerobic archaebacteria. They are hydrogen-sulfur autotrophic and grow at temperatures of up to 95°C (25). T. tenax differs from T. neutrophilus in that it can also grow heterotrophically and has an acidic pH growth optimum rather than one close to neutral (6). Their light microscopical appearance is that of extended aseptate rods of about 0.4 ,um in diameter with a length of 1.0 to 80 p.m. T. tenax often shows true branching (29). The bacteria are nonmotile and show a gram-negative staining reaction due to the simple wall architecture without a murein or pseudomurein layer (11,12,29). The walls consist of the cytoplasmic membrane and a hexagonally packed surface layer (S-layer) (22,24).We have investigated the ultrastructure and surface charge of T. tenax and T. neutrophilus, firstly to obtain information about proteins (13) which are able to withstand extreme environmental conditions and, secondly, to elucidate a possible morphogenetic function of S-layers in organisms in which paracrystalline arrays are the only component of the cell wall.MATERIALS AND METHODS Bacteria. T. tenax (DSM 2078) was isolated from a solfataric mud hole in the Kraffla area, Iceland. T. neutrophilus (DSM 2338) was isolated from a hot spring in the Kerlingarfj6ll, Iceland. Both species were grown while stirred in Allen medium (1) supplemented with 0.5% sulfur and 0.02% yeast extract. The cultures were gassed with a mixture of 80% hydrogen and 20% carbon dioxide. T. tenax was grown at pH 5.5, and T. neutrophilus was grown at pH 6.8.Materials. Cationized ferritin was purchased from Sigma Chemical Co., Munich, Federal Republic of Germany. All other chemicals used were of reagent grade.Specimen preparation. For freeze-etching, the whole bacteria were centrifuged, and 1-pl samples were immediately frozen in Freon 22 (Polaron Equipment Ltd., Watford, England) kept close to its solidification temperature * Corresp...

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Section: Resultsmentioning

confidence: 93%

Ultrastructure of the cell envelope of the archaebacteria Thermoproteus tenax and Thermoproteus neutrophilus

Messner¹,

Pum²,

Sára³

et al. 1986

J Bacteriol

141

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“…Upon transition to the nematic phase at ;46.5 °C a large number of defects or disclinations 51 were observed in all regions of the sandwich. The density of defects began to decrease immediately.…”

Section: Alignment Of Mbba In the Nematic Phasementioning

confidence: 99%

Orientation of Crystalline Overlayers on Amorphous Substrates by Artificially Produced Surface Relief Structures

Flanders¹

1978

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“…Disclinations are rarely observed in 3D structures such as metals because they are energetically very costly [18], but are seen occasionally in foams [6,7] and they often appear in block copolymers [19] and liquid crystals [16,18,[20][21][22], particularly in nematic liquid crystals. The latter typically consist of elongated molecules that tend to be oriented in the same direction, but are positionally disordered.…”

Section: Disclinationsmentioning

confidence: 99%

“…The motion can be in one of three directions: if it occurs along one of the two axes that are perpendicular to the axis of the torus, edge dislocations are obtained. If the motion is parallel to the axis of the torus, it defines a screw dislocation [18]. Only edge dislocations will be considered in this work.…”

Section: Dislocationsmentioning

confidence: 99%

“…To accommodate the wedge, the torus has to be cut from the outer edge to the hollow core. Disclinations are classified according to the relative motion of the two cut surfaces: rotation around the axis of the torus will produce a wedge disclination [18], whereas rotations around axes perpendicular to the axis of the torus will produce twist disclinations. In what follows only 2D wedge disclinations are considered.…”

Section: Disclinationsmentioning

confidence: 99%

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Simulation of defects in bubble clusters

Cox¹,

Teixeira²,

Vaz³

2010

J. Phys.: Condens. Matter

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Abstract. Topological defects in a foam, either isolated (disclinations and dislocations) or in pairs, affect the energy and stress, and play an important role in foam deformation. Surface Evolver simulations were performed on large finite clusters of bubbles. These allow us to evaluate the effect of the topology of the defects, and the distance between defects, on the energy and pressure of foam clusters of different sizes. The energy of such defects follows trends similar to known analytical results for a continuous medium.

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Disclinations

Cited by 88 publications

References 0 publications

Ultrastructure of the cell envelope of the archaebacteria Thermoproteus tenax and Thermoproteus neutrophilus

Ultrastructure of the cell envelope of the archaebacteria Thermoproteus tenax and Thermoproteus neutrophilus

Orientation of Crystalline Overlayers on Amorphous Substrates by Artificially Produced Surface Relief Structures

Simulation of defects in bubble clusters

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