Reductive dechlorination of tetrachloroethene to cis-1,2-dichloroethene bya thermophilic anaerobic enrichment culture

Thermophilic anaerobic biodegradation of tetrachloroethene (PCE) was invest igated with various inocula from geothermal and nongeothermal areas. Only p olluted harbor sediment resulted in a stable enrichment culture that Conver ted PCE via trichloroethene to cis-1,2-dichloroethene at the optimum temper ature of 60 to 65 degrees C. after several transfers, methanogens were elim inated from the culture. Dechlorination was supported by lactate, pyruvate, fructose,fumarate; and malate as electron donor but not by H-2, formate, o r acetate. Fumarate and L-malate led to the highest dechlorination rate. In the absence of PCE, fumarate was fermented to acetate, H-2, CO2, and succi nate. With PCE, less H-2 was formed, suggesting that PCE competed for the r educing equivalents leading to H-2. PCE dechlorination, apparently, was not outcompeted by fumarate as electron acceptor. At the optimum dissolved PCE concentration of similar to 60 mu M, a high dechlorination rate of 1.1 mu mol h(-1) mg(-1) (dry weight) was found, which indicates that the dechlorin ation is not a cometabolic activity. Microscopic analysis of the fumarate-g rown culture showed the dominance of a long thin rod. Molecular analysis, h owever, indicated the presence of two dominant species, both belonging to t he low-G+C gram positives. The highest similarity was found with the genus Dehalobacter (90%), represented by the halorespiring organism Dehalobacter restrictus, and with the genus Desulfotomaculum (86%).