- Volume 67, Issue 3, 1971
Volume 67, Issue 3, 1971
- Biochemistry
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The Ferredoxin-dependent Reduction of Chloramphenicol by Clostridium acetobutylicum
More LessSUMMARY: Chloramphenicol did not inhibit growth and protein synthesis when added (100 μg./ml.) to growing cultures of Clostridium acetobutylicum, even though the organism was sensitive to this antibiotic in plate assay. This paradox was explained by the finding that chloramphenicol was rapidly reduced and thus detoxified by actively growing cultures. Cell-free extracts of C. acetobutylicum reduced the aryl nitro group of chloramphenicol via a ferredoxin-dependent enzymic reaction for which pyruvate was the most effective primary electron donor. A number of other aryl nitro-compounds were similarly reduced.
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The Relationship between Prodigiosin Biosynthesis and Cyclic Depsipeptides in Serratia marcescens
More LessSUMMARY: The concentrations of lipid-bound serine (in the form of cyclic depsipeptide) and prodigiosin, in Serratia marcescens respond similarly to changes in environmental or cultural conditions so that highly pigmented cells always have a relatively large amount of lipid-bound serine. In addition, when prodigiosin synthesis is induced in non-pigmented cells, a parallel rapid synthesis of cyclic depsipeptide occurs concomitantly. Their simultaneous occurrence may indicate a common control.
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- Development And Structure
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Isolation and Characterization of Escherichia coli bacteriophage Ω8 specific for E. coli strains belonging to sero-group O8
More LessSUMMARY: A bacteriophage which is specific for Escherichia coli O8 strains was isolated from Freiburg sewage. It is designated as Ω8. Inhibition studies suggested that the O8 specific lipopolysaccharide (isolated from E. coli O8) may be the phage receptor or part of it. Bacteriophage Ω8 also causes clearing on lawns of E. coli O93 if added at high multiplicity but it does not multiply in this strain. Escherichia coli strains O8 and O93 cross-react serologically and their (O antigenic) lipopolysaccharides have similar structures. Electron microscopy revealed the following features of Ω8: icosahedric head, 48 to 50 nm. in diameter; base plate consisting of 6 units, total diameter 14 nm.; 6 spikes, 12·0 to 14·5 nm. long and 3·5 to 4·0 nm. thick; 6 fibres, 168 nm. long, bent at 56 nm., 1·5 nm. thick. The propagation characteristics of Ω8 are: burst size, 130; latent period, 19 min.; eclipse period, 13 min.
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- Genetics And Molecular Biology
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The Differential Effects of Nystatin on Growth of Auxotrophic and Prototrophic Strains of Aspergillus nidulans
More LessSUMMARY: Nystatin affects the transfer of nutrients into fungal cells. Auxotrophs of Aspergillus nidulans vary in their susceptibility to nystatin, hence it is possible that they could be used to diagnose the effects of this antibiotic on cellular transport mechanisms for the uptake of different metabolites. Nystatin treatment can select auxotrophs from a largely prototrophic population in A. nidulans because newly germinated conidia are more sensitive to nystatin than ungerminated conidia. As the mycelium of germinated conidia ages it becomes less sensitive, so that critical conditions for maximum selection are a suitable period on minimal medium agar, sufficient only for germination of prototrophs, followed by the addition of nystatin in complete medium agar at a level which preferentially kills germinated conidia, thus allowing enrichment for ungerminated auxotrophic conidia. After treatment of prototrophic conidia of A. nidulans with ultraviolet irradiation auxotrophic selection was achieved by the nystatin method.
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Drug Resistant Mutants and Appearance of Heterozygotes in the Cellular Slime Mould Dictyostelium discoideum
Y. Fukui and I. TakeuchiSUMMARY: Mutants of Dictyostelium discoideum resistant to the antifungal antibiotics, Naramycin or Trichomycin, were isolated after treatment with nitrosoguanidine. When two strains differing in pigmentation and drug resistance were cultured together, amoebae resistant to both drugs appeared in underwater cultures and in liquid shake cultures. Such heterozygotes did not appear during the growth period, but only after cultures reached stationary phase. The appearance of the heterozygotes seems to have some relationship to the state of cells. Studies on the ploidy and the resistance of the progeny of these heterozygous isolates revealed that: (1) diplophase of the original heterozygote is probably transient, (2) all the progeny observed are mononucleate, (3) the ploidy of each progeny settles in a stable state of aneuploidy (between the haploid and the diploid), (4) genetic segregants for drug resistance and pigmentation appear among the progeny in serial subcultures, (5) preferential chromosome elimination occurs during the process of chromosomal reduction. A mechanism of recombination in D. discoideum is discussed in relation to the parasexual cycle.
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- Medical Microbiology
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An Examination of the Production of Hydrolytic Enzymes and Toxins by Pathogenic Strains of Candida albicans
More LessSUMMARY: Attempts to demonstrate the production of toxin by pathogenic strains of Candida albicans have proved negative; a variety of growth conditions and methods of organism extraction were used, several of which were previously described by other workers as yielding toxins. Toxin production appears to be a strain characteristic and not a property of all pathogenic strains. Acid phosphatases with pH optima at 3·6 and 5·6, a peptidase with optimum pH 6·6 and β-glucosidase have been isolated from both blastospore and mycelial forms of C. albicans and their properties examined. The occurrence in organism extracts of alkaline phosphatase and peptidase (optimum pH 3·6) has been confirmed; no activity of mucopolysaccharase, neuraminidase, β-glucuronidase or phospholipase A and B could be demonstrated. The possible role of hydrolytic enzymes in pathogenicity is discussed.
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The Rapid Detection and Determination of Sparse Bacterial Populations with Radioactively Labelled Homologous Antibodies
More LessSUMMARY: An assay for rapidly detecting and determining sparse populations of vegetative bacteria or bacterial spores (minimum number about 500; 2 to 4 x 10−10g. equivalent bacterial dry weight) is described. A sample is treated with 125I-labelled purified homologous antibody, filtered and washed on a Millipore membrane filter, and the radioactivity of the separated labelled immune complex is measured. The assay is specific, accurate and completed within 8 to 10 min. Sensitivity and accuracy decrease if the assay is applied to samples that contain particulate matter that non-specifically attaches antibody and is retained by a membrane filter. This type of interference is decreased by pretreating samples with clarified normal rabbit serum for a few minutes before assay.
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- Physiology And Growth
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Influence of the Width of the Peripheral Growth Zone on the Radial Growth Rate of Fungal Colonies on Solid Media
More LessSUMMARY: Growth of colonies of Rhizopus stolonifer, Mucor racemosus, Actinomucor repens, Absidia glauca, Geotrichum lactis, Penicillium chrysogenum, Aspergillus wentii, A. niger and two strains of A. nidulans were studied. The radial growth rate (K r) of these colonies was found to be a function of the length (w) of the leading hyphae spanning the colony's peripheral growth zone and the specific growth rate (α) of these hyphae. Thus
K r = αw.
The peripheral growth zone is the region in which hyphae are able to contribute protoplasm to the apical extension of the colony's leading hyphae. The width of the peripheral growth zone remained constant with time but varied from 423 μm. for G. lactis to 8660 μm. for R. stolonifer. The specific growth rate of the hyphae in the colony's peripheral growth zone appeared to be identical to the organism's maximum specific growth rate in submerged culture.
The width of the peripheral growth zone was not influenced by temperature or by adding an inhibitor to the medium but did vary with glucose concentration. An observed difference between the radial growth rates of the two strains of Aspergillus nidulans, which had almost identical specific growth rates in submerged culture, was found to be correlated with a difference between the widths of their respective peripheral growth zones. Although there was a significant difference in the length of the apical cells and hyphal compartments of the leading hyphae of these strains, the growth zone of the hyphae of each strain contained 16 septa; it is suggested that the strains differ in the frequency of septum formation but not in the rate at which the septa become plugged.
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Exponential Growth of the Germ Tubes of Fungal Spores
More LessSUMMARY: The germ tubes of eight fungi studied initially grew exponentially in length. Subsequently there was a deceleration in their growth rate. With the exception of Geotrichum lactis the germ-tube specific growth rate of each organisms was substantially greater than its specific growth rate in submerged culture. The possible reason for this difference is discussed.
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- Short Communications
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- Taxonomy
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Serology of Rumen Bacteroides
More LessSUMMARY: The serological relationships of 26 strains of rumen Bacteroides species comprising Bacteroides ruminicola, B. amylophilus and B. succinogenes were examined using precipitation, agglutination and fluorescent antibody techniques. With precipitation techniques two types of acid-soluble thermostable antigens were detected, a strain-specific antigen and an antigen demonstrating wider serological relationships. With B. amylophilus and B. succinogenes this latter antigen was species-specific. With B. ruminicola, although eight out of 12 strains possessed the same species-specific antigen, there was evidence of two other serological groups within the species. Agglutination tests detected only the strain-specific antigens. Fluorescent antibody tests detected species-specific antigens of B. amylophilus and B. succinogenes but with B. ruminicola only the strain-specific antigens could be demonstrated. Preliminary work with B. ruminicola indicated that both kinds of antigen were polysaccharides. Eleven out of 20 freshly isolated strains of B. ruminicola reacted with the B. ruminicola antiserum. When 30 strains of eight other species of Bacteroides were tested against the species-specific antiserum of the different rumen species of Bacteroides, four strains of B. oralis and one strain of B. melanogenicus were found to have a common antigen with that of B. ruminicola, and another strain of B. oralis had a common antigen with another B. ruminicola strain. No other cross-reactions were observed.
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