A bphK gene encoding glutathione S-transferase (GST) activity is located in the bph operon in Burkholderia sp. strain LB400 but its role in polychlorinated biphenyl (PCB) metabolism is unknown. This gene was over-expressed in Escherichia coli and an in vivo assay based on growth of E. coli containing GST activity was used to identify potential novel substrates for this enzyme. Using this assay, 4-chlorobenzoate (4-CBA) was identified as a substrate for the BphK enzyme. High pressure liquid chromatography analysis and chloride ion detection showed removal of 4-CBA and an equivalent increase of chloride in cell extracts when incubated with this enzyme. These results would indicate that this BphK enzyme has dechlorination activity in relation to 4-CBA and may have a role in protection of other Bph enzymes against certain chlorinated metabolites of PCB degradation.