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Volume 134,
Issue 2,
1988
Volume 134, Issue 2, 1988
- Physiology And Growth
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The Surface Layer of Mycoplasma mobile 163K and Its Possible Relevance to Cell Cohesion and Group Motility
More LessMycoplasma mobile strain 163K tends to move in multicellular configurations, either as pairs or small groups of three or more cells, or as chain-like aggregations or microcolonies. Such wandering groups arise by transient association of independently moving cells. This behaviour of M. mobile was microscopically investigated and documented by sequences of microcinematographic pictures, as well as by photomicrographically recorded motility tracks. The presence of an extracellular slime layer was demonstrated in thin sections, by negative staining and by scanning electron microscopy. The possible association of this layer with the cohesive properties of the mycoplasma cells, enabling the formation of wandering groups, is discussed and a calculation of the magnitude of the cohesive force is provided.
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Induction of a Stable Morphological Change in Propionibacterium freudenreichii
More LessWhen cells of Propionibacterium freudenreichii were incubated under fasting conditions and then plated in the presence of an inhibitor of protein synthesis, a variable but significant (>10−2) fraction of the population changed their morphology from rod to sphere, with a considerable thickening of the cell wall. This change was accompanied by metabolic and antibiotic-resistance modifications, including the synthesis of at least one new enzyme (α-glucosidase), and by the simultaneous appearance of several new species of DNA, presumably plasmids. The round cells grew faster than the parent strain and maintained their morphology indefinitely when propagated on complex medium containing glucose as the main carbon source. However, when glucose was omitted, cells returned to the rod form and regained their previous characteristics, including the absence of detectable plasmids.
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Cyanophycin Granule Size Variation in Aphanocapsa
More LessTechniques were developed for the rapid and simple electron microscopic visualization of isolated cyanophycin granules to allow analysis of their size from cells grown under different conditions. Granules were purified by differential and renografin density-gradient centrifugation from cells grown for various times in chloramphenicol-containing media, or in nitrogen-limited media to which nitrogen was then added back, or under light limitation. Granules were then observed by electron microscopy after staining with uranyl acetate, and random granule diameters were measured. Granule size increased significantly with time following chloramphenicol treatment and following light limitation. This suggests that much of the increase in amount of cyanophycin in cells treated with chloramphenicol or light limitation is caused by increase in granule size rather than in granule number. Insignificant changes in granule size were observed during nitrogen repletion, suggesting increase in granule number, not size.
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A Study of the Role of the Hexose Monophosphate Pathway with Respect to Fatty Acid Biosynthesis in Sporulation of Saccharomyces cerevisiae
More Less13C NMR was used to study the pattern of label incorporation from [2-13C]acetate into trehalose during sporulation in Saccharomyces cerevisiae. A wild-type strain and a strain homozygous for the zwf1 mutation (which affects glucose-6-phosphate dehydrogenase) were used. In the wild-type it was possible to deduce the cycling of glucose 6-phosphate around the hexose monophosphate pathway whilst in the mutant strain this did not occur. The requirement of the hexose monophosphate pathway for providing NADPH for fatty acid biosynthesis was examined using 13C NMR and GC/MS. The wild-type strain produced a typical profile of fatty acids with palmitoleic acid being the most abundant whereas the mutant contained only one-quarter the amount of total fatty acid. As zwf1 homozygous diploids are able to sporulate this indicates that the large amount of fatty acid biosynthesis observed in sporulation of wild-type strains is not essential to the process.
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Lipid Turnover in Oleaginous Yeasts
More LessWhen eight strains of the oleaginous yeasts Candida curvata, Lipomyces starkeyi, Rhodosporidium toruloides and Trichosporon cutaneum were starved of carbon after having accumulated lipid up to 34% of their biomass, the lipid was readily converted to new biomass in all cases except the two strains of L. starkeyi. When C. curvata D was grown in a two-stage chemostat with the second stage as a carbon-starvation vessel (but containing NH+ 4) biosynthesis of new biomass reached 1·9 ± 0·2 g per g lipid utilized. Experiments in a single-stage chemostat undergoing transition from lipid accumulation (nitrogen-limited medium) to carbon-starvation conditions showed that the lipid in C. curvata was rapidly mobilized. When the lipid was pre-labelled with 14C, a transitory pool of rapidly metabolizable non-lipid material appeared within 1.5 h of the initiation of starvation. Rates of lipid loss indicated that initiation of lipid degradation occurred immediately carbon was lost from the external medium.
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Arachidonic Acid from Fungi Utilizing Fatty Acids with Shorter Chains as Sole Sources of Carbon and Energy
More LessSeveral species of soil fungi, belonging to the genera Aspergillus, Penicillium, Fusarium, Paecilomyces, Trichoderma, Cladosporium and Stachybotrys could utilize caprylic, myristic, palmitic, stearic and oleic acids, as well as their sodium salts, as sole sources of carbon and energy. None of the fungal isolates showed any particular specificity to a given fatty acid. Only the caprylic acid utilizers grew poorly, otherwise the growth was fair to abundant. The optimal fatty acid concentration for fungal growth was 10 g l−1. Growth yields were comparable with those on glucose. The optimal pH values were in the region of neutrality and the isolates could tolerate high acidity. Lipids from fungi grown on fatty acids or their sodium salts contained free fatty acids as the predominant lipid class. Such lipids were much richer in arachidonic acid than those from the same fungi grown on glucose. Fungi that contained the highest levels of arachidonic acid were those grown on myristic and palmitic acids, namely Aspergillus versicolor and Aspergillus ustus, respectively.
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Aminochelin, a Catecholamine Siderophore Produced by Azotobacter vinelandii
More LessA catecholamine siderophore, named aminochelin, produced by iron-limited Azotobacter vinelandii was purified and tentatively identified as 2,3-dihydroxybenzoylputrescine. This compound was first observed as an ethyl-acetate-insoluble catechol that accounted for 30 to 50% of the total catechol in iron-limited culture supernatant fluids. The purified compound was unstable at neutral to alkaline pH, bound Fe3+, Fe2+ and molybdate, and promoted 55Fe-uptake into iron-limited A. vinelandii. Aminochelin was induced and repressed coordinately with the other catechol siderophore azotochelin. The catechol siderophores were, however, less sensitive to repression by soluble iron than the yellow-green fluorescent peptide siderophore azotobactin.
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- Systematics
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Rhodothermus marinus, gen. nov., sp. nov., a Thermophilic, Halophilic Bacterium from Submarine Hot Springs in Iceland
More LessThermophilic, reddish-coloured heterotrophic bacteria different from Thermus were isolated from submarine alkaline hot springs in Iceland. The bacteria were obligately aerobic, moderately halophilic, Gram-negative rods, about 0.5 m in diameter and 2-2.5 m long. Neither spores, flagella nor lipid granules were observed, but a slime capsule was formed on carbohydrate-rich medium. Optimum growth was at 65C, pH 7.0, and at about 2% (w/v) NaCl. The bacteria were oxidase negative, catalase positive and contained a carotenoid pigment with the main absorbance peak at 476 nm and shoulders at 456 and 502 nm. The GC content of the DNA was about 64 mol%. Electron micrographs clearly showed an outer membrane, about 9 nm thick, and the cytoplasmic membrane together with the peptidoglycan layer was about 14 nm in thickness. The isolates were nutritionally different from Thermus. They utilized several common sugars but glutamate and aspartate were the only amino acids that most strains used. These bacteria are considered to represent a new genus which we name Rhodothermus, with the type species Rhodothermus marinus.
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DNA:DNA Reassociation Analysis of Aeromonas salmonicida
More LessDNA from 26 Aeromonas salmonicida strains, namely 11 ‘typical’ and 15 so-called ‘atypical’ strains, was used to assess the taxonomic relatedness within the species. The genomes were characterized by determination of DNA base composition, DNA:DNA reassociation, calculation of sequence divergence following reassociation, and by genome size estimations. By comparison with DNA obtained from controls and the Aeromonas hydrophila group, A. salmonicida strains were determined to be correctly placed with respect to genus and species. A. salmonicida subspecies salmonicida (the ‘typical’ group) was an extremely homogeneous taxon. The ‘atypical’ strains were more diverse, but distinct biotypes were recognizable. The first biotype included several geographically diverse isolates from goldfish. The second recognizable biotype included strains isolated from European carp. Other ‘atypical’ isolates could not be grouped but showed enough internal homology to be retained within the species. The A. salmonicida subspecies achromogenes and masoucida were found to be closely related to the motile aeromonads. It is considered that the present classification of A. salmonicida is unsuitable and should be restructured to include A. salmonicida subspecies salmonicida, subspecies achromogenes (to include the present subspecies masoucida), and the reintroduced subspecies nova.
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Characterization of Yersinia enterocolitica, Y. intermedia, Y. aldovae, Y. frederiksenii, Y. kristensenii and Y. pseudotuberculosis by Electrophoretic Polymorphism of Acid Phosphatase, Esterases, and Glutamate and Malate Dehydrogenases
PH. Goullet and B. PicardAcid phosphatase, esterases, and glutamate and malate dehydrogenases of 192 strains of Yersinia enterocolitica, Y. intermedia, Y. aldovae, Y. frederiksenii, Y. kristensenii and Y. pseudotuberculosis were analysed by horizontal polyacrylamide agarose gel electrophoresis and by isoelectrofocusing in thin-layer polyacrylamide gels. The six species were clearly separated from each other by their distinct enzyme electrophoretic polymorphism. For Y. enterocolitica, the strains of biotype 5 were differentiated from the other biotypes by the mobility of glutamate dehydrogenase. For Y. frederiksenii, six zymotypes were delineated by pI and by the mobility of the enzymes. Variation in number or mobility of esterases within each species could represent a marker for epidemiological and ecological analyses. A linear relationship was obtained between the mean genetic diversity coefficient of enzymes and the mean percentage DNA-DNA relatedness of Y. intermedia, Y. aldovae, Y. enterocolitica and Y. frederiksenii.
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Characteristics of Glutamate Dehydrogenase, a New Diagnostic Marker for the Genus Fusobacterium
More LessEnzymes representative of carbohydrate and nitrogen metabolism were screened for their presence and activity amongst species of the genus Fusobacterium. Glutamate dehydrogenase (GDH) was reliably detected in all 25 strains studied. The pH profile of this enzyme and the DNA base composition of selected strains were also determined. DNA base composition of selected strains ranged between 28-32.9 mol% G + C. GDH was active between pH 7.5-11.5 but two pH profiles of activity, with optima at 9.5 and 10.5, were discernible among species. Apart from Fusobacterium nucleatum, which had a heterogeneous enzyme pattern, the GDH electrophoretic mobility was constant within a species but in a few cases the enzyme bands overlapped. A combination of the pH profile, the GDH electrophoretic pattern and the DNA base composition provided clear separation of the test organisms into discrete groups; however, a larger number of strains must be examined before the full potential of these tests can be evaluated.
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