title: Stable carbon isotope fractionation of chloroethenes by dehalorespiring isolates.
abstract: Stable carbon isotope fractionation during the reductive dechlorination of chloroethenes by two bacterial strains that dechlorinate to ethene, Dehalococcoides ethenogenes 195 and Dehalococcoides sp. strain BAV1 as well as Sulfurospirillum multivorans and Dehalobacter restrictus strain PER-K23, isolates that do not dechlorinate past DCE, are reported. Fractionation by a Dehalococcoides-containing enrichment culture is also measured for comparison to the isolates. All data adequately fit the Rayleigh model and results are presented as enrichment factors. For strain 195, the measured enrichment factors were -9.6 +/- 0.4, -21.1 +/- 1.8, and -5.8 +/- 0.5 when degrading TCE, cDCE, and 1,1-DCE, respectively. Strain BAV1 exhibited enrichment factors of -16.9 +/- 1.4, -8.4 +/- 0.3, -21.4 +/- 0.9, and -24.0 +/- 2.0 for cDCE, 1,1-DCE, tDCE, and VC, respectively. The surprisingly large differences in enrichment factors caused by individual reductases (RDases) reducing different chloroethenes is likely the result of chemical structure differences among the chloroethenes. For TCE reduction, S. multivorans and D. restrictus strain PER-K23 exhibited enrichment factors of -16.4 +/- 1.5 and -3.3 +/- 0.3, respectively. While all of the organisms studied here utilize RDases that require corrinoid cofactors, the biotic TCE enrichment factors varied widely from those reported for the abiotic cobalamin-catalyzed reaction, indicating that additional factors affect the extent of fractionation in these biological systems. The enrichment factors measured for the Dehalococcoides-containing enrichment culture did not match well with those from any of the isolates, demonstrating the inherent difficulties in predicting fractionation factors of undefined communities. Although compound-specific isotope fractionation is a powerful tool for evaluating the progress of in situ bioremediation in the field, given the wide range of enrichment factors associated with functionally similar and phylogenetically diverse organisms, caution must be exercised when applying enrichment factors for the interpretation of dechlorination data.
authors.affiliation: Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720, USA.
authors.forename: Patrick K H
authors.initials: PK
authors.lastname: Lee
authors.forename: Mark E
authors.initials: ME
authors.lastname: Conrad
authors.forename: Lisa
authors.initials: L
authors.lastname: Alvarez-Cohen
mesh_terms: D001419:Bacteria / Q000302:isolation & purification / Q000378:metabolism*; D001673:Biodegradation, Environmental; D002247:Carbon Isotopes; D005591:Chemical Fractionation; D041862:Chloroflexi / Q000302:isolation & purification / Q000378:metabolism; D004000:Dichloroethylenes / Q000737:chemistry / Q000378:metabolism; D020565:Epsilonproteobacteria / Q000302:isolation & purification / Q000378:metabolism; D006843:Hydrocarbons, Chlorinated / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D010459:Peptococcaceae / Q000302:isolation & purification / Q000378:metabolism; D014241:Trichloroethylene / Q000737:chemistry / Q000378:metabolism; D014752:Vinyl Chloride / Q000737:chemistry / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000378:metabolism*
chemical_list: D002247:Carbon Isotopes; D004000:Dichloroethylenes; D006843:Hydrocarbons, Chlorinated; D014874:Water Pollutants, Chemical; D014241:Trichloroethylene; D014752:Vinyl Chloride