Aerobic dechlorination of cis- and trans-dichloroethenes by some indigenous bacteria isolated from contaminated sites in Africa

Abstract

The innate toxicity of dichloroethenes (DCEs) and their tendency to be reduced to vinyl chloride (VC) (a known human carcinogen) is a cause for environmental concern. Aerobic bacteria capable of growth on cis- and trans-DCEs as sole carbon and energy sources were isolated by enrichment culture technique and identified to belong to the genera; Bacillus, Pseudomonas and Acinetobacter. Axenic and mixed cultures of the bacterial isolates utilized DCEs at concentrations above the maximum contaminant level allowable in drinking water by the Environmental Protection Agency. Their specific growth rate constant ranged significantly (P < 0.05) between 0.346-0.552 and 0.461-0.667 d(-1); while the maximum specific substrate utilization rate ranged significantly (P < 0.05) between 20.01-29.79 and 31.40-42.83 nmol h(-1) (mg of protein)(-1) in cis- and trans-DCE, respectively. The optimum growth was observed at 30 degrees C and at a pH of 7.0 with up to 96% of the stoichiometric-expected chloride released. Serial adaptation positively affected the growth yields and dehalogenase activities of the organisms with multiple antibiotic patterns also demonstrated by the isolates. These findings therefore indicated the important roles that these organisms may play in the bioremediation of sites polluted with chlorinated ethene compounds in Africa.