Kurt W. Hanselmann

Identification of a microcystin in benthic cyanobacteria linked to cattle deaths on alpine pastures in Switzerland

During the last two decades, more than 100 cattle deaths have been reported from 11 alpine sites in south-eastern Switzerland. Pathological findings and the histological examination of their organs strongly indicated acute hepatotoxicosis. Clinical symptoms suggestive of neurotoxicity were also observed in some cases. To elucidate the etiology of these poisonings, different water bodies in one of the affected alpine pastures were investigated for cyanobacterial toxins. The waters were highly oligotrophic, cold and turbid, and the ice-free period was limited to 3–4 months. The algal community in these waters consisted mostly of benthic cyanobacteria forming dense mats on the surface of sediments and on submerged rocks. Oscillatoria limosa and Phormidium konstantinosum (=Oscillatoria tenuis) dominated these populations, but occasionally other species of Oscillatoria, Phormidium, Tychonema and Pseudanabaena also occurred in the mats. Samples from the cyanobacterial mats yielded positive results in a protein ...

Similarities between the Abiotic Reduction of Selenite with Glutathione and the Dissimilatory Reaction Mediated by Rhodospirillum rubrum and Escherichia coli

Various mechanisms have been proposed to explain the biological dissimilatory reduction of selenite (\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{SeO}_{3}^{2-}\) \end{document}) to elemental selenium (Se°), although none is without controversy. Glutathione, the most abundant thiol in the eukaryotic cells, the cyanobacteria, and the α, β, and γ groups of the proteobacteria, has long been suspected to be involved in selenium metabolism. Experiments with the phototrophic α proteobacterium Rhodospirillum rubrum showed that the rate of selenite reduction was decreased when bacteria synthesized lower than normal levels of glutathione, and in Rhodobacter sphaeroides and Escherichia coli the reaction was reported to induce glutathione reductase. In the latter organism superoxide dismutase was also induced in cells grown in the presence of selenite, indicating that superoxide anions (O-2) were produced. These observations led us to investigate the abiotic (chemical) reduction of selenite by glutathione and to compare the features of this reaction with those of the reaction mediated by R. rubrum and E. coli. Our findings imply that selenite was first reduced to selenodiglutathione, which reached its maximum concentration within the 1st min of the reaction. Formation of selenodiglutathione was paralleled by a rapid reduction of cytochrome c, a known oxidant for superoxide anions. Cytochrome c reduction was inhibited by superoxide dismutase, indicating that O-2 was the source of electrons for the reduction. These results demonstrated that superoxide was produced in the abiotic reduction of selenite with glutathione, thus lending support to the hypothesis that glutathione may be involved in the reaction mediated by R. rubrum and E. coli. The second phase of the reaction, which led to the formation of elemental selenium (Se°), developed more slowly. Se° precipitation reached a maximum within 2 h after the beginning of the reaction. Secondary reactions leading to the degradation of the superoxide significantly decreased the yield of Se° in the abiotic reaction compared with that of the bacterially mediated selenite reduction. Abiotically formed selenium particles showed the same characteristic orange-red color, spherical structure, and size as particles produced by R. rubrum, again providing support for the hypothesis that glutathione is involved in the reduction of selenite to elemental selenium in this organism.

Fermentative metabolism of substituted monoaromatic compounds by a bacterial community from anaerobic sediments

AbstractAn anaerobic microbial community containing 4 to 5 different populations capable of degrading syringic acid completely to CH4 and CO2 was enriched from freshwater lake sediments. The community can be maintained with syringic acid as sole carbon- and energy source in a defined mineral medium. Syringic acid is converted stoichiometrically according to

Evaluation and application of dialysis porewater samplers for microbiological studies at sediment-water interfaces

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The meromictic alpine Lake Cadagno: Orographical and biogeochemical description

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Localisation of the subunits of the photosynthetic reaction centers in the chromatophore membrane of Rhodospirillum rubrum.

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Environmental conditions in high mountain lakes containing toxic benthic cyanobacteria

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Comparison of different substrates for the fast reductive dechlorination of trichloroethene under groundwater conditions

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Biomass composition and methods for the determination of metabolic reserve polymers in phototrophic sulfur bacteria

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