title: Reductive dechlorination of TCE by chemical model systems in comparison to dehalogenating bacteria: insights from dual element isotope analysis (13C/12C, 37Cl/35Cl).
abstract: Chloroethenes like trichloroethene (TCE) are prevalent environmental contaminants, which may be degraded through reductive dechlorination. Chemical models such as cobalamine (vitamin B12) and its simplified analogue cobaloxime have served to mimic microbial reductive dechlorination. To test whether in vitro and in vivo mechanisms agree, we combined carbon and chlorine isotope measurements of TCE. Degradation-associated enrichment factors ε(carbon) and ε(chlorine) (i.e., molecular-average isotope effects) were -12.2‰ ± 0.5‰ and -3.6‰ ± 0.1‰ with Geobacter lovleyi strain SZ; -9.1‰ ± 0.6‰ and -2.7‰ ± 0.6‰ with Desulfitobacterium hafniense Y51; -16.1‰ ± 0.9‰ and -4.0‰ ± 0.2‰ with the enzymatic cofactor cobalamin; -21.3‰ ± 0.5‰ and -3.5‰ ± 0.1‰ with cobaloxime. Dual element isotope slopes m = Δδ(13)C/ Δδ(37)Cl ≈ ε(carbon)/ε(chlorine) of TCE showed strong agreement between biotransformations (3.4 to 3.8) and cobalamin (3.9), but differed markedly for cobaloxime (6.1). These results (i) suggest a similar biodegradation mechanism despite different microbial strains, (ii) indicate that transformation with isolated cobalamin resembles in vivo transformation and (iii) suggest a different mechanism with cobaloxime. This model reactant should therefore be used with caution. Our results demonstrate the power of two-dimensional isotope analyses to characterize and distinguish between reaction mechanisms in whole cell experiments and in vitro model systems.
authors.affiliation: Institute of Groundwater Ecology, Helmholtz Zentrum München, Ingolstädter Landstrasse 1, 85764 Neuherberg, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Cretnik
authors.forename: Kristen A
authors.initials: KA
authors.lastname: Thoreson
authors.forename: Anat
authors.initials: A
authors.lastname: Bernstein
authors.forename: Karin
authors.initials: K
authors.lastname: Ebert
authors.forename: Daniel
authors.initials: D
authors.lastname: Buchner
authors.forename: Christine
authors.initials: C
authors.lastname: Laskov
authors.forename: Stefan
authors.initials: S
authors.lastname: Haderlein
authors.forename: Orfan
authors.initials: O
authors.lastname: Shouakar-Stash
authors.forename: Sarah
authors.initials: S
authors.lastname: Kliegman
authors.forename: Kristopher
authors.initials: K
authors.lastname: McNeill
authors.forename: Martin
authors.initials: M
authors.lastname: Elsner
mesh_terms: D001673:Biodegradation, Environmental; D002247:Carbon Isotopes / Q000737:chemistry; D002713:Chlorine / Q000737:chemistry / Q000378:metabolism; D045858:Desulfitobacterium / Q000378:metabolism; D045302:Geobacter / Q000378:metabolism; D007554:Isotopes / Q000737:chemistry; D009942:Organometallic Compounds / Q000737:chemistry; D010084:Oxidation-Reduction; D014241:Trichloroethylene / Q000737:chemistry* / Q000378:metabolism*; D014805:Vitamin B 12 / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D002247:Carbon Isotopes; D007554:Isotopes; D009942:Organometallic Compounds; D014874:Water Pollutants, Chemical; C556179:cobaloxime; D014241:Trichloroethylene; D002713:Chlorine; D014805:Vitamin B 12