Small (13)C/(12)C fractionation contrasts with large enantiomer fractionation in aerobic biodegradation of phenoxy acids.
Phenoxy acid herbicides are important groundwater contaminants. Stable isotope analysis and enantiomer analysis are well-recognized approaches for assessing in situ biodegradation in the field. In an aerobic degradation survey with six phenoxyacetic acid and three phenoxypropionic acid-degrading bacteria we measured (a) enantiomer-specific carbon isotope fractionation of MCPP ((R,S)-2-(4-chloro-2-methylphenoxy)-propionic acid), DCPP ((R,S)-2-(2,4-dichlorophenoxy)-propionic acid), and 4-CPP ((R,S)-2-(4-chlorophenoxy)-propionic acid); (b) compound-specific isotope fractionation of MCPA (4-chloro-2-methylphenoxyacetic acid) and 2,4-D (2,4-dichlorophenoxyacetic acid); and (c) enantiomer fractionation of MCPP, DCPP, and 4-CPP. Insignificant or very slight (ε = -1.3‰ to -2.0‰) carbon isotope fractionation was observed. Equally small values in an RdpA enzyme assay (εea = -1.0 ± 0.1‰) and even smaller fractionation in whole cell experiments of the host organism Sphingobium herbicidovorans MH (εwc = -0.3 ± 0.1‰) suggest that (i) enzyme-associated isotope effects were already small, yet (ii) further masked by active transport through the cell membrane. In contrast, enantiomer fractionation in MCPP, DCPP, and 4-CPP was pronounced, with enantioselectivities (ES) of -0.65 to -0.98 with Sphingomonas sp. PM2, -0.63 to -0.89 with Sphingobium herbicidovorans MH, and 0.74 to 0.97 with Delftia acidovorans MC1. To detect aerobic biodegradation of phenoxypropionic acids in the field, enantiomer fractionation seems, therefore, a stronger indicator than carbon isotope fractionation.
Institute of Groundwater Ecology , Helmholtz Zentrum München, Ingolstadter Landstr. 1, 85764 Neuherberg, Germany.
Shiran
S
Qiu
Erkin
E
Gözdereliler
Philip
P
Weyrauch
Eva C Magana
EC
Lopez
Hans-Peter E
HP
Kohler
Sebastian R
SR
Sørensen
Rainer U
RU
Meckenstock
Martin
M
Elsner
D015084:2,4-Dichlorophenoxyacetic Acid / Q000737:chemistry / Q000302:isolation & purification; D000332:Aerobiosis; D001419:Bacteria / Q000201:enzymology / Q000378:metabolism*; D001673:Biodegradation, Environmental; D002247:Carbon Isotopes / Q000032:analysis; D005591:Chemical Fractionation; D057075:Enzyme Assays; D006540:Herbicides / Q000737:chemistry / Q000302:isolation & purification; D010642:Phenoxyacetates / Q000737:chemistry / Q000302:isolation & purification*; D013237:Stereoisomerism
D002247:Carbon Isotopes; D006540:Herbicides; D010642:Phenoxyacetates; D015084:2,4-Dichlorophenoxyacetic Acid