Dechlorination of pesticides by a speciflc bacterial glutathione-S-transferase, BphKLB400:: Potential for bioremediation

The. bphK gene located in the bph operon of Burkholderia xenovorans LB400 encodes a protein, BphK(LB400), with significant sequence similarity to glutathione S-transferases (GSTs). GSTs are a superfamily of enzymes involved in the detoxification of many endobiotic and xenobiotic substances. Recently, BphK(LB400) was shown to catalyze the dechlorination of a number of toxic chlorinated organic compounds. Comparison of the amino acid sequence of BphK(LB400) with GSTs from other bacteria that degrade polychlorinated biphenyls identified a number of highly conserved amino acids in the C-terminal region of the protein thought to be associated with substrate specificity. Mutating the conserved amino acid at position 180 of BphK(LB400) from an alanine to a proline residue resulted in an increase in GST activity of bacterial cell extracts towards a number of chlorinated organic substrates tested including commonly used pesticides. Laboratory scale plant protection experiments suggested that E. coli expressing BphK(LB400) [wild-type and mutant (Ala180Pro)] could protect pea plants from the effects of chloromequat chloride. Therefore, BphK(LB400), identified as having dechlorination activity towards toxic chlorinated organic compounds used in the environment, could have potential in bioremediation.