Reductive dechlorination of tetrachloroethene to trans-dichloroethene and cis-dichloroethene by PCB-dechlorinating bacterium DF-1.

Polychlorinated biphenyls (PCBs) and chlorinated ethenes (CEs) are known to pollute sediment, soil, and groundwater. The anaerobic dechlorination of these compounds is an integral part of their biodegradation in polluted environments. We report for the first time the dechlorination of tetrachloroethene (PCE) and trichloroethene (TCE) by bacterium DF-1. This PCB and chlorobenzene dechlorinating bacterium dechlorinated PCE to TCE, which was then converted into trans-1,2-dichloroethene (trans-DCE) and cis-1,2-dichloroethene (cis-DCE). The ratio of trans-DCE to cis-DCE produced by the culture had a range of 1.2-1.7. Bacterium DF-1 has been enriched in co-culture with a desulfovibrio-like microorganism. PCR-denaturing gradient gel electrophoresis (PCR-DGGE) analysis of the 16S rRNA genes of the co-culture demonstrated that DF-1 was enriched during the dechlorination of PCE, PCB, and chlorobenzene. DF-1 was not detected in the absence of PCE dechlorination and the desulfovibrio-like organism, isolated in pure culture, did not dechlorinate PCE. This is the first identification of a microorganism capable of producing high amounts of trans-DCE from PCE and indicates that microorganisms such as DF-1 are a possible biological source of trans-DCE in the environment.