EVIDENCE THAT FORMATION OF PROTOANEMONIN FROM METABOLITES OF 4-CHLOROBIPHENYL DEGRADATION NEGATIVELY AFFECTS THE SURVIVAL OF 4-CHLOROBIPHENYL-COMETABOLIZING MICROORGANISMS

A rapid decline in cell viability of different PCB-metabolizing organi sms 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 th e natural microflora, Potential metabolites of 4-chlorobiphenyl, 4-chl orobenzoate and 4-chlorocatechol, caused similar toxic effects. We tes ted the hypothesis that the toxic effects are due to the formation of protoanemonin, a plant-derived antibiotic, which is toxic to microorga nisms and which has been shown to be formed from 4-chlorocatechol by e nzymes of the 3-oxoadipate pathway. Consistent with our hypothesis, ad dition to soil microcosms of strains able to reroute intermediary 4-ch lorocatechol from the 3-oxoadipate pathway and into the meta-cleavage pathway or able to mineralize 4-chlorocatechol by a modified or tho-cl eavage 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, Thi s rapid degradation accounts for our inability to detect this compound in soils amended,vith 4-chlorocatechol, However, significant accumula tion of protoanemonin was observed by a mixed bacterial community enri ched with benzoate or a mixture of benzoate and 4-methylbenzoate, prov iding the metabolic potential of the soil to form protoanemonin. The e ffects 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.