Enantioselective Uptake and Degradation of the Chiral Herbicide Dichlorprop [( RS )-2-(2,4-Dichlorophenoxy)propanoic acid] by Sphingomonas herbicidovorans MH

Abstract

Sphingomonas herbicidovorans MH was able to completely degrade both enantiomers of the chiral herbicide dichlorprop [(RS)-2-(2,4-dichlorophenoxy)propanoic acid], with preferential degradation of the (S) enantiomer over the (R) enantiomer. These results are in agreement with the recently reported enantioselective degradation of mecoprop [(RS)-2-(4-chloro-2-methylphenoxy)propanoic acid] by this bacterium (C. Zipper, K. Nickel, W. Angst, and H.-P. E. Kohler, Appl. Environ. Microbiol. 62:4318–4322, 1996). Uptake of (R)-dichlorprop, (S)-dichlorprop, and 2,4-D (2,4-dichlorophenoxyacetic acid) was inducible. Initial uptake rates of cells grown on the respective substrate showed substrate saturation kinetics with apparent affinity constants (Kt ) of 108, 93, and 117 μM and maximal velocities (V max) of 19, 10, and 21 nmol min−1 mg of protein−1 for (R)-dichlorprop, (S)-dichlorprop, and 2,4-D, respectively. Transport of (R)-dichlorprop, (S)-dichlorprop, and 2,4-D was completely inhibited by various uncouplers and by nigericin but was only marginally inhibited by valinomycin and by the ATPase inhibitorN,N′-dicyclohexylcarbodiimine. Experiments on the substrate specificity of the putative transport systems revealed that (R)-dichlorprop uptake was inhibited by (R)-mecoprop but not by (S)-mecoprop, (S)-dichlorprop, or 2,4-D. On the other hand, the (S)-dichlorprop transport was inhibited by (S)-mecoprop but not by (R)-mecoprop, (R)-dichlorprop, or 2,4-D. These results provide evidence that the first step in the degradation of dichlorprop, mecoprop, and 2,4-D by S. herbicidovorans is active transport and that three inducible, proton gradient-driven uptake systems exist: one for (R)-dichlorprop and (R)-mecoprop, another for (S)-dichlorprop and (S)-mecoprop, and a third for 2,4-D.

Selective transport and accumulation of alkanes by Rhodococcus erythropolis S+14He

“…Another explanation is slower mass transfer for utilization at decreasing n-hexadecane concentrations. An analogous case is the enantioselective uptake and degradation of the chiral herbicide dichlorprop by Sphingomonas herbicidovorans MH (Zipper et al, 1998). The energy-driven selective uptake of (S)dichlorprop from enantiomeric mixtures gave lower growth rates compared to cells grown on the pure S-isomer compound.…”

Aerobic biodegradation of chiral phenoxyalkanoic acid derivatives during incubations with activated sludge

“…Furthermore, accumulation of enantiomers may increase the toxicity of enantiomer mixtures, due to di¡erent toxicities of the single enantiomers. Enantioselective biodegradation of stereoisomers is based on (i) the selective uptake of enantiomers by microorganisms as reported for the xylose enantiomers [17] and for (R)-and (S)-dichlorprop [6]; (ii) the selective intracellular metabolism of stereoisomers as demonstrated for the initial metabolism of (R)-and (S)-mecoprop by soil isolates [18,19]; (iii) di¡erent rates of biologically mediated enantiomerization for the (R) and the (S) enantiomers as shown for the stereoisomers of mecoprop and dichlorprop in soil [20,21]. Extracellular enantiomerization could be excluded in our study since the concentrations of (S)-PPA, (S)-2-CPPA, and (S)-fenoprop did not increase during biodegradation of (R)-PPA, (R)-2-CPPA, and (R)-fenoprop ( Fig.…”

“…In order to test and understand the microbial degradation of racemic mixtures of chiral organic compounds, the DOC measurements need to be complemented by enantiomer-speci¢c analysis, because the length of the lag phases as well as the degradation rates may di¡er for the enantiomers. We have reported previously the enantioselective degradation of the chiral herbicides mecoprop [(RS)-2-(4-chloro-2-methylphenoxy)propanoic acid] and dichlorprop [(RS)-2-(2,4-dichlorophenoxy)propanoic acid] by Sphingomonas herbicidovorans MH [5,6] and upon incubation with aerobic sewage sludge [7]. Both the (R) and the (S) enantiomers were completely metabolized but the (S) enantiomers were removed from the test medium before the (R) enantiomers.…”

Seasonal Fluctuations of Bacterial Community Diversity in Agricultural Soil and Experimental Validation by Laboratory Disturbance Experiments

“…Strain MH is able to grow on phenoxyalkanoic acid herbicides, such as mecoprop (2-(4-chloro-2-methylphenoxy)propionic acid), as sole carbon and energy source [20]. The strain was grown at 30°C in 5 mL complex medium [46] in baffled Erlenmeyer flasks shaken at 180 rpm. Cells were harvested during the exponential phase, centrifuged for 5 min at 7,500×g, washed once with phosphate-buffered saline (PBS; the solution contains 137 mM NaCl, 2.7 mM KCl, 4.3 mM Na 2 HPO 4 7H 2 O, 1.4 mM KH 2 PO 4 , pH 7.3) to remove nutrients, and pelleted again by centrifugation.…”