Comamonas testosteroni JH5 used 4-chlorophenol (4-CP) as its sole source of energy and carbon up to a concentration of 1.8 mM, accompanied by the stoichiometric release of chloride. The degradation of 4-CP mixed with the isomeric 2-CP by resting cells led to the accumulation of 3-chlorocatechol (3-CC), which inactivated the catechol 2,3-dioxygenase. As a result, further 4-CP breakdown was inhibited and 4-CC accumulated as a metabolite. In the crude extract of 4-CP-grown cells, catechol 1,2-dioxygenase and muconate cycloisomerase activities were not detected, whereas the activities of catechol 2,3-dioxygenase, 2-hydroxymuconic semialdehyde dehydrogenase, 2-hydroxymuconic semialdehyde hydrolase, and 2-oxopent-4-enoate hydratase were detected. These enzymes of the meta cleavage pathway showed activity with 4-CC and with 5-chloro-2hydroxymuconic semialdehyde. The activities of the dioxygenase and semialdehyde dehydrogenase were constitutive. Two key metabolites of the meta cleavage pathway, the meta cleavage product (5-chloro-2-hydroxymuconic semialdehyde) and 5-chloro-2-hydroxymuconic acid, were detected. Thus, our previous postulation that C. testosteroni JH5 uses the meta cleavage pathway for the complete mineralization of 4-CP was confirmed. The aerobic microbial degradation of many aromatic compounds occurs via catechols as key metabolites. The breakdown of catechols proceeds via the central step of ortho or meta ring fission. In general, methyl-substituted aromatic compounds are degraded via the meta cleavage pathway, whereas xenobiotics like chloroaromatic compounds are mineralized via the ortho cleavage pathway (9, 21). The degradation of methyl-and chloroaromatic substrates in mixture is often incomplete, leading to the accumulation of dead-end metabolites like chlorocatechols, chlorinated hydroxymuconic semialdehydes, or 4-carboxymethyl-methylbut-2-en-1,4-olides (31, 33). As a possible metabolite of chloroaromatic breakdown, 3-chlorocatechol (3-CC) reversibly inhibits the meta-cleaving catechol 2,3-dioxygenase or totally blocks the meta cleavage pathway by the irreversible suicide inactivation of this dioxygenase (4, 16, 20). Recently, we described Comamonas testosteroni JH5, which completely mineralizes a mixture consisting of 4-chlorophenol (4-CP) and monomethylphenols (16). The degradation of 4methylphenol (4-MP) and 4-CP occurred successively. Mixtures consisting of 4-CP and 2-MP or 3-MP were mineralized simultaneously. Since a catechol 2,3-dioxygenase, but no orthocleaving enzyme, was detected in cells grown on 4-CP, the mineralization of 4-CP via meta ring fission was postulated (16). Furthermore, a Pseudomonas species is able to completely mineralize 5-chlorovanillate via meta cleavage (18). Kersten et al. (18) showed that the formed acylchloride undergoes cyclization, which leads to a spontaneous removal of the chloride substituent. This mechanism is restricted to orthosubstituted halogens and therefore would not work with 4-CP. Recently, the meta cleavage of 4-chlorobenzoate by Pseudomonas cepacia ...

Comamonas testosteroni JH5 was isolated from a mixed bacterial culture enriched on different chloro-and methylphenols. The strain completely mineralized a mixture consisting of 4-chlorophenol (4-CP) and 4-methylphenol (4-MP). During degradation of the mixture, 4-hydroxybenzyl alcohol, 4-hydroxybenzaldehyde, 4-hydroxybenzoic acid, and 4-chlorocatechol were detected as short-lived intermediates. Mineralization of 4-CP and that of 4-MP occurred successively and were accompanied by diauxic growth, whereas 4-CP and 2-methylphenol were mineralized simultaneously. It was ascertained that neither a reversible enzyme inhibition nor potential toxic intermediates caused the observed diauxie. Some facts support the hypothesis that the successive degradation of 4-CP and 4-MP is regulated on the level of transcription. C. testosteroni JH5 contained a meta-cleaving enzyme when pregrown on 4-CP and the isomeric monomethylphenols. Inactivation of this enzyme in the presence of 3-chlorocatechol was observed.

ZusammenfassungIn Zeiten multipler sozialer, ökologischer und ökonomischer Krisen sieht sich die Ökonomie, insbesondere aber die ökonomische Bildung durch die studentische Kritik an ihrer Weltfremdheit, Abstraktheit und ethischen Unschärfe zur Verantwortung gerufen. Im vorliegenden Beitrag berichten die Autorinnen von ihren Erfahrungen bei der Umsetzung einer dezidiert weltzugewandten ökonomischen Bildung. Diese rückt den Kontext wirtschaftlichen Denkens und Handelns auf der einen und das erkennende und sich bildende Subjekt auf der anderen Seite in den Mittelpunkt des Bildungsgeschehens. Am Beispiel der einwöchigen Exkursion von Ökonomiestudierenden der Cusanus Hochschule für Gesellschaftsgestaltung in das landwirtschaftliche Ensemble von Rothenklempenow legen die Autorinnen die didaktische Umsetzung dieses Bildungsanliegens dar.