Browsing by Author "Schmid, Andreas"

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Open Access
Der Abbau von Modellstrukturen der Kohle: Stoffwechselweg des Dibenzofuran- und Fluorenabbaus
(1991) Engesser, Karl-Heinrich; Strubel, Volker; Trenz, Stefan Peter; Rothe, Bernd; Schmid, Andreas; Knackmuss, Hans-Joachim
Several microorganisms have been isolated degrading structural elements of coal like dibenzofuran. fluorene and biphenyl. Extensive investigation of the degradation pathways revealed a common mechanism of initial attack. Although catalyzed by different enzymes, all three substrates are converted to 3-phenyl-substituted catechols, which, after meta-cleavage are transformed to simple aromatic structures like salicylate, phthalate and benzoate. This ring cleaving enzymes have been cloned and are further analyzed after subcloning. Two different initial dioxygenases seem to be present in some strains cataIyzing ether cleavage of dibenzofuran and oxygenation of biphenyl respectively. Attempts are presently made to clone the first enzyme in order to produce higher yields of its optically active products. Some of these compounds have been characterized and may be of commercial value as fine chemicals.
Open Access
Einsatz von Gensonden zur Identifikation von Mikroorganismen im belebten Schlamm
(1994) Engesser, Karl-Heinrich; Schmid, Andreas
Die Gensondentechnik stellt heute schon einen extrem leistungsfähigen, neuartigen Ansatz zur Populationsanalyse komplexer Ökosysteme und damit auch der Charakterisierung der "Biomasse" des Belebtschlammes dar. Für die Gensondentechnik typisch ist ein relativ geringer Zeitaufwand bei der Durchführung. Dies ermöglicht erstmals die Analyse der Dynamik einer Population nahezu in Echtzeit.
Open Access
Microbial degradation of model compounds of coal and production of metabolites with potential commercial value
(1994) Engesser, Karl-Heinrich; Dohms, Christian; Schmid, Andreas
Due to the need of new strategies for improving the economical performance of coal technologies, efforts were undertaken to develop techniques of solubilizing coal by the action of microorganisms. Because of the poor information in the beginning of this research, the microbial metabolism of some monomeric structural elements of coal was investigated first. Dibenzofuran, for example, was chosen as it represents a model structure frequently found in many coals, i.e. the cyclic biarylether moiety. It was found to be degraded by many different organisms isolated from soil via a new degradative mechanism called "angular" dioxygenation. Fluorene, a model compound for dibenzo-cyclopentane structures in coal, surprisingly followed essentially the same metabolic steps. Additional compounds which were integrated in the research program like naphthalenes, biphenyls, biarylethers and carbazoles also exhibited an oxygenase-dependent mode of initial attack. Since all enzymes involved were not active outside the cells, there seems to be no way to employ them in biological depolymerisation of untreated coals. Current work therefore, by employing special selection substrates, concentrates on the detection of new enzyme systems which follow non-oxygenase dependent mechanisms. In a second line of research the enzyme systems mentioned above are used to synthesize new organic compounds from coal-derived substances. Due to the relaxed substrate specifity of the initial dioxygenases many structural analogues of dibenzofuran are metabolized. Several optically active compounds of the dihydrodiol-type were isolated and characterized by spectroscopic methods. We recently developed a preparative technique to produce these potentially valuable metabolites at a gram-scale. In addition, methods of genetic engineering are currently being adopted to create stable high expression organisms with improved productivity.
Open Access
Tumor cell invasion and gap junctional communication. 1, Normal and malignant cells confronted in monolayer cultures
(1990) Bräuner, Thomas; Schmid, Andreas; Hülser, Dieter F.
Mammary tumor cells of the rat (BICR/MIR k) and mouse (EMT6/Ro) as well as rat glioma cells (C6) are electrically coupled and show intercellular dye spreading. Monolayer cultures of synchronously beating chicken heart cells were also electrically coupled, dye spreading. however, was significantly restricted to only one or two adjacent cells. In all coupled cells, gap junctions were found in both freeze-fracture replicas and ultrathin sections. Heterologous gap junctional coupling between these tumor cells and heart cells was regularly established. The human cervix carcinoma line Hela and the mouse L sarcoma line were elcctrically not coupled and did not reveal gap junctions, consequently they showed no coupling to heart cells.