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Biomedical subjects

S C Holt

Publications and source records attributed to S C Holt.

At least 163 records · Page 9Linked to original sources
PubMed1974

Ultrastructure of hamster kidney cell culture infected with Herpesvirus.

Hamster kidney cell culture was found susceptible to infection and replication of herpesvirus of turkey (HVT) as evidenced by cytopathic effect, induction of HVT-specific, complement-fixing antigen, and demonstration of virus particles by electron microscopy. Viral structures at different developmental stages were observed. Several infected cells showed a lamellar inclusion body possibly continuous with the endoplasmic reticulum. The function of these lamellar bodies is not known.

Animals↗
PubMed1974

Biogenesis of Marek's disease (type II leukosis) virus in vitro: electron microscopy and immunological study.

The kinetic events involved in Marek's disease herpesvirus infection of avian cell culture were investigated by assaying viral infectivity and antigenicity as well as by electron microscopy during the infectious cycle. The levels of viral infectivity and complement-fixing (CF) antigens revealed that the rates of appearance of infectious particles and CF antigens were not synchronous. Viral specific CF antigen could be detected 5 h after infection, whereas viral infectivity or the appearance of viral particles could be demonstrated only after 10 h of infection. High proportions of the recovered CF antigens during the various stages of the infectious cycle were found to be soluble and did not sediment with the virus particles. Cytological analysis of the developmental stages of the JM virus-infected cells by thin sectioning and electron microscopy revealed that at 8 h small particles approximately 35 nm in diameter appeared in the cell nuclei. The appearance of nucleocapsids occurred at 10 h, and these were of varying shapes; however, all were approximately 100 nm in diameter. At approximately 18 h postinfection, mature virus particles were observed. Viral maturation of the immature particles occurred by the acquisition of envelope from the inner leaflet of the nuclear membrane or from the cytoplasmic membrane of the cell.

Animals↗
PubMed1974

Cold lability of Bacillus cereus bacteriophage CP-51.

Phage CP-51 was rapidly inactivated when stored at the usual refrigerator temperatures (2 to 4 C) and even more rapidly when exposed to 0 C. The loss in viability resulting from exposure to cold appeared to correlate with the increase in number of phage particles having contracted tails. High concentrations (0.01 M) of Mg(2+), Ca(2+), or Mn(2+) stabilized the phage considerably, but even in the presence of these divalent cations, it was much less stable at 0 C than at 15 C.

Bacillus cereus↗
PubMed1973

Ultrastructural properties of the extra membranes of Escherichia coli O111a as revealed by freeze-fracturing and negative-staining techniques.

Escherichia coli O111a is a thermosensitive strain which, when grown at 40 C, accumulates large quantities of intracellular membranes. The ultrastructure of these membranes in cells which have been chemically fixed, embedded, and examined as thin sections has been compared with that of membranes in cells negatively stained or freeze-fractured. Results indicate that the extra membranes are present in the three types of preparations examined and, therefore, clearly are not artifacts of chemical fixation. Negative staining has proved also to be a valuable tool as a rapid means of monitoring cells for the accumulation of large amounts of extra membranes. Also, examination of thin sections has shown that distinct continuities between the plasma membrane and the extra membranes exist. In general, membrane surfaces in freeze-fractured cells containing extra membranes appear smooth and lack the particles associated with the plasma membranes of many cells.

Cell Membrane↗
PubMed1973

Role of glutathione in the morphogenesis of the bacterial spore coat.

There is a marked increase in the half-cystine content of bacterial spores, especially the coat layers at the time of formation of the outer coat. When a cysteine auxotroph of Bacillus cereus T is grown on limiting cysteine, the spores contain the normal content of half-cystine, suggesting an alternate source. Glutathione appears to be such a supply of cysteine since it is hydrolyzed during sporulation and there are increased activities of the hydrolyzing enzymes at the same time. In addition, a cysteine auxotroph with a second alteration, a temperature-sensitive glutathione disulfide reductase, produces lysozyme-sensitive spores at 40 C. These spores appear to be defective in the formation of outer spore coat. During sporulation at 40 C, the double mutant accumulates oxidized glutathione which is a poor substrate for the hydrolytic enzymes. As a result, sporulating cells are deficient in half-cystines which are essential for outer spore coat morphogenesis. This alteration can be overcome by a shift to 30 C or by addition of cystinyl-pencillamine or cysteinyl-glycine to cultures sporulating at 40 C.

Bacillus cereus↗
PubMed1973

Peptidoglycan of free-living anaerobic spirochetes.

Electron microscope examination of negatively stained or thin-sectioned cells of Spirochaeta stenostrepta treated with penicillin or lysozyme showed that the peptidoglycan was present as a thin, electron-dense layer adjacent and external to the cytoplasmic membrane. The peptidoglycan was isolated from cells of S. stenostrepta and Spirochaeta litoralis by a procedure including treatments with sodium lauryl sulfate and Pronase. Hydrolysates of the isolated S. stenostrepta and S. litoralis peptidoglycans contained glucosamine, muramic acid, glutamic acid, l-ornithine, and alanine in molar ratios of 0.90:0.85:1.00:1.00:1.40 and of 0.63:0.63:0.99:1.00:1.41, respectively. Determination of N-terminal residues suggested that nearly 50% of the ornithine in S. stenostrepta and S. litoralis peptidoglycans was involved in peptide cross-linkage. The peptidoglycan layer of S. stenostrepta was sensitive to lysozyme and myxobacter AL-1 protease.

Alanine↗
PubMed1971

Regulation of extracellular protease production in Bacillus cereus T: characterization of mutants producing altered amounts of protease.

Twenty-nine mutants of Bacillus cereus T were selected on casein agar for their inability to produce large amounts of extracellular protease. They all formed spores, and 27 were also auxotrophs for purines or pyrimidines. Upon reversion to prototrophy, a large fraction regained the capacity to produce protease. Conversely, reversion to normal protease production resulted in loss of the purine or pyrimidine requirement in a large fraction of the revertants. One spontaneous low-protease-producing pyrimidine auxotroph studied in detail grew as well as the wild type and produced spores which were identical to those produced by the wild type on the basis of heat resistance, dipicolinic acid content, density, and appearance in the electron microscope. The rate of protein turnover in the mutant was the same as the wild type. The mutant did grow poorly, however, when casein was the principal carbon source. A mutant excreting 5 to 10 times as much protease as the wild type was isolated as a secondary mutation from the hypoproducer discussed above. Loss of the pyrimidine requirement in this case did not alter the regulation of protease production. Although the secondary mutant grew somewhat faster in most media than the wild type, the final cell yield was lower. The spores of this mutant appeared to have excess coat on the basis of both electron microscopic and chemical studies. There appear to be closely related but distinct catabolic controls for both extracellular protease and spore formation. These controls can be dissociated as for the hypoproducers but can also appear integrated as for the hyperprotease producer.

Agar↗
PubMed1970

The effect of 3-(3,4-dichlorophenyl)-1,1-dimethylurea on chloroplast development and maintenance in Euglena gracilis. I. Ultrastructural characterization of light-grown cells by the techniques of thin sectioning and freeze-etching.

The ultrastructure of light-grown Euglena gracilis var. bacillaris was examined by the techniques of thin sectioning and freeze-etching. Thin sectioning revealed the typical organelles previously observed in chemically fixed Euglena. In addition to confirming the observations on thin sections, the freeze-etch technique has revealed the presence in E. gracilis of a complex multilaminar pellicle, and an ordered arrangement to the paramylon granule. The chloroplast thylakoids are particulate and similar to those observed in higher plants.

Chloroplasts↗
PubMed1969

Purification, ultrastructure, and composition of axial filaments from Leptospira.

The ultrastructure of three strains of water Leptospira was studied by negative staining, thin sectioning, and freeze-etching. The cells possessed a triple-layered sheath which covered two independent axial filaments, one inserted subterminally in each end of the cell. The protoplasmic cylinder was surrounded by a triple-layered cell wall and possessed ribosomes, lamellar structures, and a typical procaryotic nuclear region. The axial filament was comprised of several component structures. An axial fibril, with a diameter of 20 to 25 nm, consisted of a solid inner core (13 to 16 nm in diameter) surrounded by a coat. A terminal knob (40 to 70 nm in length) was connected to a series of disc insertion structures at the terminal end of the axial fibril. The axial fibril was surrounded by a helical outer coat (35 to 60 nm in diameter) which was composed of a continuously coiled fiber, 3 to 4 nm in diameter, embedded in an electron-dense material. A procedure for the purification of the axial fibrils was presented and their ultrastructural, physical, and chemical properties were determined. Similarities in ultrastructural, physical, and chemical properties were noted between the axial fibrils and bacterial flagella. A schematic model of the leptospiral axial filament is presented, and a mechanism is proposed for its function as a locomotor organelle.

Amino Acids↗
PubMed1968

Fine structure of Spirochaeta stenostrepta, a free-living, anaerobic spirochete.

The fine structure of Spirochaeta stenostrepta strain Z1, a free-living anaerobic spirochete, was studied by electron microscopy. The organism possessed a coiled protoplasmic cylinder, an axial filament inserted subterminally, and a loosely fitting sheath which enclosed both the protoplasmic cylinder and the axial filament. The axial filament consisted of two fibrils partially overlapping in a 1-2-1 arrangement. The axial fibrils appeared to possess a sheath surrounding an inner core. Both inner core and sheath were apparently enclosed in a cross-striated tubular structure, which was itself surrounded by an outer sheath. The axial filament exhibited a basal hook. A disc- or mushroom-shaped structure, possibly consisting in part of cytoplasmic membrane, was observed at the insertion end of isolated filaments. The protoplasmic cylinder had a distinctive surface structure consisting of an array of tightly packed, longitudinally arranged helices measuring 2.0 to 2.5 nm in diameter. This layer of helices lay below the outer cell sheath and the axial filament. Ballistic disintegration loosened the helical array, causing individual helices or segments of helices to become separated from the cell. The function of this layer of helices is still obscure.

Cytoplasm↗
PubMed1968

Cytology of spore formation in Clostridium perfringens.

The sequential morphological events in spore formation by Clostridium perfringens type D were observed in Ellner's medium where 80 to 100% of the cells formed spores. Gross structural changes were studied with the light microscope under phase-contrast, and in fixed cells by the use of both nigrosin and Giemsa preparations. Fine structure was examined with the electron microscope in both thin sections and frozen-etched preparations. During the first 3 hr of incubation, the original rod-shaped cells became ellipsoid to ovoid in shape; by 5 to 6 hr, subterminal spores had developed within these enlarged cells. The fine structural sequence was in most respects identical to that in other Bacillaceae, although some stages were illustrated with particular clarity. A unique feature was the development of a convoluted, membranous exosporium which adhered to the outer surface of the two coats and had an unusual fine structure resembling a rectangular array of subunits.

Clostridium perfringens↗