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| - Variations in 13C/12C and D/HEnrichment Factors of AerobicBacterial Fuel OxygenateDegradation
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| - Reliable compound-specific isotope enrichment factorsare needed for a quantitative assessment of in situbiodegradation in contaminated groundwater. To obtaininformation on the variability on carbon and hydrogenenrichment factors (εC, εH) the isotope fractionation ofmethyl tertiary (tert-) butyl ether (MTBE) and ethyl tert-butyl ether (ETBE) upon aerobic degradation was studiedwith different bacterial isolates. Methylibium sp. R8showed a carbon and hydrogen isotope enrichment uponMTBE degradation of −2.4 ± 0.1 and −42 ± 4‰,respectively, which is in the range of previous studieswith pure cultures (Methylibium petroleiphilum PM1) aswell as mixed consortia. In contrast, εC of the β-proteobacterium L108 (−0.48 ± 0.05‰) and Rhodococcus ruberIFP 2001 (−0.28 ± 0.06‰) was much lower and hydrogenisotope fractionation was negligible (εH ≤ −0.2‰). Thevarying isotope fractionation pattern indicates that MTBEis degraded by different mechanisms by the strains R8and PM1 compared to L108 and IFP 2001. The carbon andhydrogen isotope fractionation of ETBE by L108 (εC =−0.68 ± 0.06‰ and εH = −14 ± 2‰) and IFP 2001 (εC =−0.8 ± 0.1‰ and εH = −11 ± 4‰) was very similarand seemed slightly higher than the fractionation observedupon MTBE degradation by the same strains. The lowcarbon and hydrogen enrichment factors observed duringMTBE and ETBE degradation by L108 and IFP 2001suggest a hydrolysis-like reaction type of the ether bondcleavage compared to oxidation of the alkyl group assuggested for the strains PM1 and R8. The variability ofcarbon and hydrogen enrichment factors should be takeninto account when interpreting isotope pattern of fueloxygenates with respect to biodegradation in contaminationplumes.
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