Carbon Isotope Fractionation during Aerobic Biodegradation of Trichloroethene by Burkholderia cepacia G4: a Tool To Map Degradation Mechanisms

Abstract

The strain Burkholderia cepacia G4 aerobically mineralized trichloroethene (TCE) to CO 2 over a time period of ϳ20 h. Three biodegradation experiments were conducted with different bacterial optical densities at 540 nm (OD 540 s) in order to test whether isotope fractionation was consistent. The resulting TCE degradation was 93, 83.8, and 57.2% (i.e., 7.0, 16.2, and 42.8% TCE remaining) at OD 540 s of 2.0, 1.1, and 0.6, respectively. ODs also correlated linearly with zero-order degradation rates (1.99, 1.11, and 0.64 mol h ؊1 ). While initial nonequilibrium mass losses of TCE produced only minor carbon isotope shifts (expressed in per mille ␦ 13 C VPDB ), they were 57.2, 39.6, and 17.0‰ between the initial and final TCE levels for the three experiments, in decreasing order of their OD 540 s. Despite these strong isotope shifts, we found a largely uniform isotope fractionation. The latter is expressed with a Rayleigh enrichment factor, , and was ؊18.2 when all experiments were grouped to a common point of 42.8% TCE remaining. Although, decreases of to ؊20.7 were observed near complete degradation, our enrichment factors were significantly more negative than those reported for anaerobic dehalogenation of TCE. This indicates typical isotope fractionation for specific enzymatic mechanisms that can help to differentiate between degradation pathways.

Monitoring Oxidation of Chlorinated Ethenes by Permanganate in Groundwater Using Stable Isotopes: Laboratory and Field Studies

“…Poulson and Naraoka (22) created a headspace in their bottles and thus part of the TCE was in the gaseous phase where no oxidation occurs, while in this study completely filled bottles were used. This could lead to more negative δ 13 C values in the gaseous phase compared to the aqueous phase and thus to smaller calculated isotopic enrichment factors.…”

“…According to the Rayleigh equation (28), the isotopic composition of the reactant is given by where f is the fraction of reactant remaining, RS is the isotope ratio of reactant at a remaining fraction f, RSo is the initial isotope ratio of the reactant, and R is the fractionation factor. The fractionation factor is defined by (28) where dP13, dP12 are increments of product containing 13 C and 12 C, respectively, which appear at an infinitely short time (instantaneous product) and S13, S12 are the concentration of reactant with 13 C and 12 C, respectively.…”

“…By using the δ 13 C notation for carbon isotope ratios and the relationship that links the fractionation factor R to the isotopic enrichment factor , ) (R -1)‚1000, eq 1 transforms to where δ 13 CS is the carbon isotope ratio of the reactant at a remaining fraction f and δ 13 CSo is the initial carbon isotope ratio of the reactant. In this study, isotope fractionation is expressed as isotopic enrichment factors.…”

Compound-specific stable isotope analysis of organic contaminants in natural environments: a critical review of the state of the art, prospects, and future challenges

“…"Identification and quantification of biodegradation processes") that, with the few exceptions mentioned above, are nowadays limited to online δ 13 C measurements (e.g., see refs. [98,99,100,101,102]). …”

Groundwater Strategy for the Ou-1 Landfill Area, Miamisburg Closure Project, Ohio

“…Despite these large effects, the carbon isotope ratio of ethene in all these wells reached the carbon isotope ratios of the initial dissolved TCE, confirming the complete conversion of dissolved TCE to ethene. Other recent studies have demonstrated that stable isotopic fractionation by aerobic cometabolic bacteria is greater then for anaerobic bacteria demonstrating the stable isotopic analyses of TCE and CO 2 can differentiate the dominant pathway in the environment that is degrading TCE or PCE (Barth et al, 2002). While these techniques are new they provide direct evidence of the biodegradation of PCE and TCE that is occurring in situ and thus are excellent measures for validation bioremediation and natural attenuation.…”