Stereospecific degradation of the phenoxypropionate herbicide dichlorprop

2,4-Dichlorophenoxyacetic acid (2,4-D)/alpha-ketoglutarate (alpha-KG) dioxy genase, TfdA, from Ralstonia eutropha JMP134, was purified from recombinant cells and shown by gas chromatographic and colorimetric methods to degrade only the S enantiomer of dichlorprop, a phenoxypropionate herbicide. Simil arly, cell extracts of Burkholderia cepacia RASC, containing a biochemicall y and genetically related alpha-KG-dependent dioxygenase, also were shown t o oxidize (S)-dichlorprop using chiral HPLC and colorimetric methods. In co ntrast, cell extracts of a mecoprop-degrading strain of Alcaligenes denitri ficans were shown to catabolize (R)-dichlorprop. Although the A. denitrific ans activity exhibited stereospecificity opposite to that of the JMP134 and RASC strains, its cofactor requirements were found to be characteristic of an alpha-KG-dependent dioxygenase. A PCR amplification product from the DN A of this strain was shown to encode an amino acid sequence that was 95% an d 86% identical to the corresponding region of TfdA in RASC and JMP134, res pectively. Thus, closely related herbicide-degrading gene products appear t o be capable of exhibiting opposite stereochemical degradative capabilities . (C) 1999 Elsevier Science B.V. All rights reserved.