title: Effects of trace element concentration on enzyme controlled stable isotope fractionation during aerobic biodegradation of toluene.
abstract: The effects of iron concentration on carbon and hydrogen isotopic fractionation during aerobic biodegradation of toluene by Pseudomonas putida mt-2 were investigated using a low iron medium and two different high iron media. Mean carbon enrichment factors (epsilonc) determined using a Rayleigh isotopic model were smaller in culture grown under high iron conditions (epsilonc = -1.7+/-0.1%) compared to low iron conditions (epsilonc = -2.5+/-0.3%). Mean hydrogen enrichment factors (epsilonH) were also significantly smaller for culture grown under high iron conditions (epsilonH = -77 +/-4%) versus low iron conditions (EpsilonH = -159+/-11%). A mechanistic model for enzyme kinetics was used to relate differences in the magnitude of isotopic fractionation for low iron versus high iron cultures to the efficiency of the enzymatic transformation. The increase of carbon and hydrogen enrichment factors at low iron concentrations suggests a slower enzyme-catalyzed substrate conversion step (k2) relative to the enzyme-substrate binding step (k-l) at low iron concentration. While the observed differences were subtle and, hence, do not significantly impact the ability to use stable isotope analysis in the field, these results demonstrated that resolvable differences in carbon and hydrogen isotopic fractionation were related to low and high iron conditions. This novel result highlights the need to further investigate the effects of other trace elements known to be key components of biodegradative enzymes.
authors.affiliation: Stable Isotope Laboratory, Department of Geology, University of Toronto, 22 Russell Street, Toronto, Canada M5S 3B12.
authors.forename: Silvia A
authors.initials: SA
authors.lastname: Mancini
authors.forename: Sarah K
authors.initials: SK
authors.lastname: Hirschorn
authors.forename: Martin
authors.initials: M
authors.lastname: Elsner
authors.forename: Georges
authors.initials: G
authors.lastname: Lacrampe-Couloume
authors.forename: Brent E
authors.initials: BE
authors.lastname: Sleep
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Edwards
authors.forename: Barbara Sherwood
authors.initials: BS
authors.lastname: Lollar
mesh_terms: D000332:Aerobiosis; D004798:Enzymes / Q000378:metabolism*; D007554:Isotopes; D007700:Kinetics; D016958:Pseudomonas putida / Q000201:enzymology / Q000378:metabolism*; D014050:Toluene / Q000378:metabolism*; D014131:Trace Elements / Q000032:analysis*
chemical_list: D004798:Enzymes; D007554:Isotopes; D014131:Trace Elements; D014050:Toluene