Dehalogenation of dioxins and chlorophenols
 
 

The lab of Ute Lechner
 

contact projects members of the group publications

 

PROJECTS

 

1.    Reductive dehalogenation of chlorinated biaryls and other chloroaromatics by enrichment cultures from anoxic river sediments of Sachsen-Anhalt   Introduction Due to their lipophilic character, highly chlorinated organic molecules show a long persistence in the environment and tend to accumulate in food chains. Further, they often accumulate in anoxic areas like deeper soil layers or river and lake sediments. So far, the only known mechanism for the transformation of these compounds under anoxic conditions is a stepwise elimination of chloroatoms by reductive dehalogenation. This produces products which are better water soluble and bio-degradable, e.g. by aerobic microbial processes. Reductive dehalogenation is used by various anaerobic bacteria for energy transduction in an anaerobic respiration mode which is called "dehalorespiration". In the region around the old industrial site Bitterfeld (Middle Germany), some river sediments are highly contaminated with chloroorganic compounds like dibenzo-p-dioxins, chlorobenzenes and chlorophenols. We enrich dechlorinating bacteria out of these sediments and characterize the process in more detail. We use less toxic dioxin congeners and chlorobenzenes for our studies.   Aims - Elucidation of the regiospecificity of dechlorination by the aid of GC/ECD- and GC/MS-analyses and assessment of the long term behaviour and toxicity of pollutants in contaminated sediments. - Characterization of the composition of microbial consortia with molecular ecological methods like fluorescense in situ hybridization using genus or species specific 16S rRNA probes, amplification of 16S rRNA genes from the mixed cultures and characterization by terminal restriction fragment length polymorphism (t-RFLP), restriction analysis (ARDRA) and sequencing. - Enrichment and isolation of the bacteria responsible for dechlorination and their physiological, biochemical and taxonomic characterization. 2.    Studies on Desulfitobacterium and Dehalococcoides Introduction The first description of the grampositive endospore-forming genus Desulfitobacterium was published in 1994. Since that time, five species with several strains are known. Most of them can carry out reductive dechlorination of chloroaromatic or chloroaliphatic compounds, thereby using this process for dehalorespiration. A chlorophenol-dehalogenating strain D. hafniense TCP-A was isolated by us from sediment of the river Saale. To date, the genus Dehalococcoides comprises only two known pure cultures consisting of very small bacteria with an unusual  morphology and outstanding physiology. Growth of these bacteria strictly depends on dehalorespiration with either tetrachloroethene or chlorobenzene. Recently, we demonstrated that one of these bacteria is even able to dechlorinate dioxins. Using molecular methods, Desulfitobacterium and Dehalococcoides were often detected in anaerobic zones contaminated with chlorinated compounds. Thus, these organisms are highly relevant for detoxification, i.e. regarding the nowadays often discussed accelerated environmental self detoxification (natural attenuation). However, the prerequisite for this process is the in situ viability and activity of these organisms. The dehalogenating activity against contaminants might depend on several factors such as the inducibility and specificity of dehalogenases. Aims Dehalococcoides: - Identification of dehalogenase genes in a dioxin dehalogenating strain - Transcription analysis in response to different chlorinated compounds using the microarray technology - Identification of “natural” substrates of the dehalogenases which promote growth of the bacterium Desulfitobacterium: Some strains of Desulfitobacterium contain large insertions in their 16S rRNA genes, which could be of interest for the specific detection of these bacteria in the environment. To date, nothing is known about the fate and function of these intervening sequences in the 16S rDNA in Desulfitobacterium. - Sequence analysis of the multiple 16S rRNA genes and their insertions in D. hafniense strain TCP-A - Analysis of 16S rDNA transcription and stability of the transcripts in the ribosomes under different growth conditions   3. Biodegradation of methyl tert-butyl ether (MTBE) by aerobic bacteria Introduction MTBE has been used as oxygenating compound in gasoline since ca 25 years. MTBE possesses a low taste and odor threshold and is a possible human carcinogen. Due to its extensive use, freshwater resources have been impacted by MTBE through accidental spills and leaking of storage tanks. In close cooperation with the Environmental Research Centre (UFZ) Leipzig-Halle, we investigate MTBE-degrading aerobic bacteria isolated from a MTBE-contaminated groundwater in Leuna. Aims - Taxonomic description of the isolates, which constitute a new genus and new species within the Betaproteobacteria - Determination of the frequency of these bacteria in contaminated groundwater at the Leuna site and the response of cell number to different remediation strategies using fluorescence in situ hybridization (FISH) and other molecular methods - Elucidation of the degradation pathway: role of a carbon-skeleton rearranging enzyme transforming the tertiary alkyl moiety into a straight carbon chain, which is finally channelled to the tricarboxylic acid cycle   MEMBERS OF THE GROUP Ute Lechner, PhD, group leader Phone:  +49 345 55 26353 (office), Fax:   +49 345 55 27010 E-mail: u.lechner@mikrobiologie.uni-halle.de   Anke Wagner (PhD student) room 204, phone: +49 345 5526355     Uwe Rauschert (student) room 212, phone: +49 345 5526354   Danny Brodkorb (student) room 204, phone: +49 345 5526355     Jana Junick (student) room 204, phone: +49 345 5526355     Marco Fischer (student) room 204, phone: +49 345 5526355   Erhard Jöx, Dr. (associated) room 217.2, phone: +49 345 5526374   Barbara Zessin, technical assistant room 212, phone: +49 345 5526354   PUBLICATIONS Bunge, M., Kähkönen, M. A., Rämisch, W., Opel, M., Vogler, S., Walkow, F., Salkinoja-Salonen, M. and Lechner, U. (2006) Biological activity in a heavily organohalogen-contaminated river sediment. ESPR – Environ. Sci. Pollut. Res., OnlineFirst (DOI: http://dx.doi.org/10.1065/espr2006.03.298). Rohwerder, T., Breuer, U., Benndorf, D., Lechner, U. and Müller, R. H. (2006) The alkyl tert-butyl ether intermediate 2-hydroxyisobutyrate is degraded via a novel cobalamin-dependent mutase pathway. Appl. Environ. Microbiol. 72, in press Ballerstedt, H., Hantke, J., Bunge, M., Werner, B., Gerritse, J., Andreesen, J. R., and Lechner, U. (2004) Properties of a trichlorodibenzo-p-dioxin-dechlorinating mixed culture with a Dehalococcoides as a putative dehalogenating species. FEMS Microbiol. Ecol. 47, 223-234. Bunge, M., Adrian, L., Kraus, A., Opel, M., Lorenz, W. G., Andreesen, J. R., Görisch, H., Lechner, U. (2003) Reductive dehalogenation of chlorinated dioxins by an anaerobic bacterium, Nature 421, 357-360 Breitenstein, A., Wiegel, J., Haertig, C., Weiss, N., Andreesen, J. R., Lechner, U. (2002) Reclassification of Clostridium hydroxybenzoicum as Sedimentibacter hydroxybenzoicus gen. nov., comb. nov. and description of Sedimentibacter saalensis sp. nov. Int. J. Syst. Evol. Microbiol. 52, 801-807. Breitenstein, A., Saano, A., Salkinoja-Salonen, M., Andreesen, J. R., Lechner, U. (2001) Analysis of a 2,4,6-trichlorophenol-dehalogenating mixed culture and isolation of the dehalogenating member Desulfitobacterium frappieri strain TCP-A. Arch. Microbiol. 175, 133-142. Bunge, M., Ballerstedt, H., Lechner, U. (2001) Regiospecific dechlorination of spiked tetra- and trichlorodibenzo-p-dioxins by anaerobic bacteria from PCDD/F-contaminated Spittelwasser sediments. Chemosphere, 43, 675-681. Bunge, M, Lechner, U. (2001) Anaerobic transformation of dioxins by bacteria from contaminated sediments: diversity of the dehalogenating community. In: Schriftenreihe des Sonderforschungsbereiches 193 der Technischen Univeristät Berlin „Biologische Behandlung industrieller und gewerblicher Abwässer", Bd. 15: Anaerobic dehalogenation, S. 69-81. Bunge, M., Werner, B., Lechner, U. (2000) Properties of a dioxin-dechlorinating microbial consortium from an acidic sulfate-rich river sediment. Organohalogen Compounds, 45, 456-459. Bunge, M., Ballerstedt, H., Lechner, U. (1999) Different regioselectivities of reductive dioxin-dechlorination by anaerobic bacteria from river sediments of the Bitterfeld district. Organohalogen Compounds 41, 387-390. Fritsche, K., Lechner, U. (1999). Defluvibacter lusatiae gen. nov., sp. nov., a new chlorophenol-degrading member of the -2 subgroup of the Proteobacteria. System. Appl. Microbiol. 22, 197-204. Ballerstedt, H., Werner, B., Gerritse, J., Lechner, U. 1998. Anaerobic bacteria from sediments dechlorinate dioxin congeners. In: Microbiology of polluted aquatic ecosystems, pp. 58-64 (Becker, P. M., ed.). Proceedings of the workshop held at UFZ, Leipzig 4.-5. Dec. 1997. Fritsche, K., Lechner, U. 1998. Molecular biology of chlorophenol degradation catalyzed by a bacterium of the Rhizobiaceae group. In: Microbiology of polluted aquatic ecosystems, pp. 102-108 (Becker, P. M., ed.). Proceedings of the workshop held at UFZ, Leipzig 4.-5. Dec. 1997. Ballerstedt, H., Kraus, A., Lechner, U. 1997. Reductive dechlorination of 1,2,3,4-tetrachlorodibenzo-p-dioxin and its products by anaerobic mixed cultures from Saale river sediment. Environ. Sci. Technol. 31, 1749-1753. Makdessi, K., Lechner, U. 1997. Purification and characerization of 2,4-dichlorophenol hydroxylase isolated from a bacterium of the alpha-2 subgroup of the Proteobacteria. FEMS Microbiol. Lett. 157, 95-101. Lechner, U., Baumbach, R., Becker, D., Kitunen, V., Auling, G., Salkinoja-Salonen, M. 1995. Degradation of 4-chloro-2-methylphenol by an activated sludge isolate and its taxonomic description. Biodegradation 6, 83-92.