Enrichment of hexachlorobenzene and 1,3,5-trichlorobenzene transforming bacteria from sediments in Germany and Vietnam

Bacterial cultures were enriched from sediments in Germany and Vietnam reductively dechlorinating hexachlorobenzene and the highly persistent 1,3,5-trichlorobenzene to monochlorobenzene. The main products of the reductive dechlorination of hexachlorobenzene were monochlorobenzene and dichlorobenzenes (1,2-; 1,3- and 1,4-dichlorobenzene) while no trichlorobenzenes accumulated. For the reductive dechlorination of 1,3,5-trichlorobenzene with the mixed culture from Vietnam sediment, 1,3- dichlorobenzene and monochlorobenzene were produced as intermediate and final end-product, respectively. The pattern of dechlorination did not change when the cultures were repeatedly exposed to oxygen over seven transfers demonstrating oxygen tolerance of the dechlorinating bacteria. However, reductive dechlorination of 1,3,5-trichlorobenzene was inhibited by vancomycin at a concentration of 5 mg L^?1. Vancomycin delayed reductive dechlorination of hexachlorobenzene in mixed cultures by about 6 months. When repeatedly applied, vancomycin completely abolished the ability of the mixed culture to transform hexachlorobenzene. Sensitivity to vancomycin and insensitivity to brief exposure of oxygen indicates that the dechlorinating bacteria in the mixed cultures did not belong to the genus Dehalococcoides.