Anaerobic microorganisms enriched from Rhine River sediments are able to remove chlorine substituents from poly‐chlorinated dibenzo‐p‐dioxines (PCDDs). A model PCDD, 1,2,3,4‐tetrachlorodibenzo‐p‐dioxin (1,2,3,4–TeCDD) was reduc‐tively dechlorinated to both 1,2,3–and l,2,4–trichlorodibenzo‐/>‐dioxins (1,2,3–and 1,2,4–TrCDD). These compounds were further dechlorinated to 1,3–and 2,3–dichlorodibenzo‐p‐dioxins and traces of 2–monochlorodibenzo‐p‐dioxin. This is the first report in the literature of the anaerobic microbial dechlorination of PCDDs. The same enrichment culture was previously found to deSchlorinate chlorinated benzenes (CBs) and polychlorinated biphenyls (PCBs). An anaerobic culture able to remove aryl chlorines from three classes of compounds has not been reported before. The rate at which the culture dechlorinates 1,2,3,4–TeCDD (t1/2 = 15.5 d) was between those observed for CBs and PCBs. This study shows that reductive dechlorination may have an effect on PCDDs in sediments, as has been demonstrated for CBs and PCBs. The formation of metabolites with a conserved 2,3‐substitution pattern from 1,2,3,4–TeCDD indicates that dechlorination of highly chlorinated dibenzo‐p‐dioxins may result in metabolites that are potentially more toxic than the parent compounds.

Due to their persistence, haloaromatics are compounds of environmental concern. Aerobically, bacteria degrade these compounds by mono- or dioxygenation of the aromatic ring. The common intermediate of these reactions is (halo)catechol. Halocatechol is cleaved either intradiol (ortho-cleavage) or extradiol (meta-cleavage). In contrast to ortho-cleavage, meta-cleavage of halocatechols yields toxic metabolites. Dehalogenation may occur fortuitously during oxygenation. Specific dehalogenation of aromatic compounds is performed by hydroxylases, in which the halo-substituent is replaced by a hydroxyl group. During reductive dehalogenation, haloaromatic compounds may act as electron-acceptors. Herewith, the halosubstituent is replaced by a hydrogen atom.

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(1997). Aerobic degradation of polychlo-rinated biphenyls by Alcaligenes sp. JB1: metabolites and enzymes. Biodegradation, (7), 435-443. General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Key words: aerobic, biodegradation, enzymes, induction, polychlorinated biphenyls, resting-cell assay AbstractIn contrast to the degradation of penta-and hexachlorobiphenyls in chemostat cultures, the metabolism of PCBs by Alcaligenes sp. JB1 was shown to be restricted to PCBs with up to four chlorine substituents in resting-cell assays. Among these, the PCB congeners containing ortho chlorine substituents on both phenyl rings were found to be least degraded. Monochloro-benzoates and dichlorobenzoates were detected as metabolites. Resting cell assays with chlorobenzoates showed that JB1 could metabolize all three monochlorobenzoates and dichlorobenzoates containing only meta and para chlorine substituents, but not dichlorobenzoates possessing an ortho chlorine substituent. In enzyme activity assays, meta cleaving 2,3-dihydroxybiphenyl 1,2-dioxygenase and catechol 2,3-dioxygenase activities were constitutive, whereas benzoate dioxygenase and ortho cleaving catechol 1,2-dioxygenase activities were induced by their substrates. No activity was found for pyrocatechase II, the enzyme that is specific for chlorocatechots. The data suggest that complete mineralization of PCBs with three or more chlorine substituents byAlcaligenes sp. JB1 is unlikely.Abbreviations: PCB -polychlorinated biphenyls, CBA -chlorobenzoate, D -di-, Tr -tri-, Te -tetra-, Pe -penta-, H -hexa

Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. A mixture of nine polychlorinated biphenyl (PCB) congeners with four to six chlorine substituents was cometabolized in an aerobic chemostat culture of Alcaligenes sp. JB1, grown on 3-methylbenzoate. Pseudo-first-order biodegradation rate constants (kb) were calculated using a steady-state kinetic model. These rate constants varied from 7.8 to 0.44 h-'. Comparable resultsfor exposure to high and low influent concentrations confirmed the assumption of pseudofirst-order kinetics for most of the congeners studied. Alcaligenessp. JB1 was found to degrade 2,3-dichlorophenyl rings very rapidly and 2,5-dichlorophenyl rings relatively slowly. Certain penta-and hexachlorobiphenyls were degraded faster than some tetrachlorobiphenyls. For example, 2,2' ,3,3' ,6,6' -hexachlorobiphenyl was degraded faster than 2,2' ,6,6' -tetrachlorobiphenyl. On the other hand, 2,2',3,3',4,4'-HCB was degraded much more slowly than 2,2',3,3'-TCB. A control experiment with Pseudomonas fluorescens NCTC10038, a bacterium incapable of PCB (co)metabolism, showed that losses caused by physical or chemical phenomena were negligible. L A E T I T I A C . M . C O M M A N D E U R , * H A N S E . V A N E Y S E R E N , M A A R T E N R . O P M E E R , H A R R I E A . J . G O V E R S , A N D J O H N R . P A R S O N S

Chromosomal DNA fragments encoding the ability to utilize biphenyl as sole carbon source (Bph+) were mobilized by means of plasmid RP4::Mu3A from strain JB1 (tentatively identified as Burkholderia sp.) to Alcaligenes eutmphus CH34 at a frequency of 10" per transferred plasmid. The mobilized DNA integrated into the recipient chromosome or was recovered as catabolic prime plasmids. Three Bph+ prime plasmids were transferred from A. eutmphus to Escherichia coli and back to A. eutmphus without modification of the phenotype. The transferred Bph+ DNA segments allowed metabolism of biphenyl, 2-,3-and cGchlorobipheny1, and diphenylmethane. Genes involved in biphenyl degradation were identified on the prime plasmids by DNA-DNA hybridization and by gene cloning. Bph+ prime plasmids were transferred t o Burkholderia cepacia, Pseudomonas aenrginosa, Comamonas testostemni and A. eutrophus and the catabolic genes were expressed in those hosts. Transfer of the plasmid to the 3-chlorobenzoate-degrading bacterium Pseudomonas sp. B13 allowed the recipient to mineralize 3-chlorobiphenyl. Other catabolic prime plasmids were obtained from JB1 by selection on m-hydroxybenzoate and tyrosine as carbon sources. 165 rRNA sequence data demonstrated that the in vivo transfer of bph was achieved between bacteria belonging to two different branches of the PProteobacteria.

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