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Appl. Environ. Microbiol., Feb 1997, 427-434, Vol 63, No. 2
R Blasco, M Mallavarapu, R Wittich, KN Timmis and DH Pieper
A rapid decline in cell viability of different PCB-metabolizing organisms
was observed in soil microcosms amended with 4-chlorobiphenyl. The toxic
effect could not be attributed to 4-chlorobiphenyl but was due to a
compound formed from the transformation of 4-chlorobiphenyl by the natural
microflora. Potential metabolites of 4-chlorobiphenyl, 4-chlorobenzoate and
4-chlorocatechol, caused similar toxic effects. We tested the hypothesis
that the toxic effects are due to the formation of protoanemonin, a
plant-derived antibiotic, which is toxic to microorganisms and which has
been shown to be formed from 4-chlorocatechol by enzymes of the
3-oxoadipate pathway. Consistent with our hypothesis, addition to soil
microcosms of strains able to reroute intermediary 4-chlorocatechol from
the 3-oxoadipate pathway and into the meta-cleavage pathway or able to
mineralize 4-chlorocatechol by a modified ortho-cleavage pathway resulted
in reversal of this toxic effect. Surprisingly, while direct addition of
protoanemonin influenced both the viability of fungi and the microbial
activity of the soil microcosm, there was little effect on bacterial
viability due to its rapid degradation. This rapid degradation accounts for
our inability to detect this compound in soils amended with
4-chlorocatechol. However, significant accumulation of protoanemonin was
observed by a mixed bacterial community enriched with benzoate or a mixture
of benzoate and 4-methylbenzoate, providing the metabolic potential of the
soil to form protoanemonin. The effects of soil heterogeneity and microcosm
interactions are discussed in relation to the different effects of
protoanemonin when applied as a shock load and when it is produced in small
amounts from precursors over long periods.
Copyright © 1997, American Society for Microbiology
Evidence that Formation of Protoanemonin from Metabolites of 4-Chlorobiphenyl Degradation Negatively Affects the Survival of 4-Chlorobiphenyl-Cometabolizing Microorganisms
Department of Microbiology, GBF-National Research Centre for Biotechnology, 38124 Braunschweig, Germany
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