In vitro dehalogenation of tetrachloroethylene (PCE) by cell-free extractsof Clostridium bifermentans DPH-1

Cell-free extracts of Clostridium bifermentans DPH-I catalyzed tetrachloroe thylene (PCE) dechlorination. PCE degradation was stimulated by addition of a variety of electron donors. Ethanol (0.61 mM) was the most effective ele ctron donor for PCE dechlorination. Maximum activity was recorded at 30 deg reesC and pH 7.5. Addition of NADH as a cofactor stimulated enzymatic activ ity but the activity was not stimulated by addition of metal ions. When the cell-free enzyme extract was incubated in the presence of titanium citrate as a reducing agent, the dehalogenase was rapidly inactivated by propyl io dide (0.5 mM). The activity of propyl-iodide-reacted enzyme was restored by illumination with a 250 W lamp. The dehalogenase activity was also inhibit ed by cyanide. The substrate spectrum of activity included trichloroethylen e(TCE), cis-1,2-dichloroethylene (cDCE), trans-dichloroethylene, 1,1-dichlo roethylene. 1,2-dichloroethane, and 1,1.2-trichloroethane. The highest rate of degradation of the chlorinated aliphatic compounds was achieved with PC E, and PCE was principally degraded via TCE to cDCE. Results indicate that the dehalogenase could play a vital role in the breakdown of PCE as well as a variety of other chlorinated aliphatic compounds. (C) 2001 Elsevier Scie nce Ltd. All rights reserved.