Reductive Dechlorination of Tetrachloroethene to cis-1,2-Dichloroethene by a Thermophilic Anaerobic Enrichment Culture

Thermophilic anaerobic biodegradation of tetrachloroethene (PCE) was investigated with various inocula from geothermal and nongeothermal areas. Only polluted harbor sediment resulted in a stable enrichment culture that converted PCE via trichloroethene to cis-1,2-dichloroethene at the optimum temperature of 60 to 65°C. After several transfers, methanogens were eliminated from the culture. Dechlorination was supported by lactate, pyruvate, fructose, fumarate, and malate as electron donor but not by H(2), formate, or acetate. Fumarate and l-malate led to the highest dechlorination rate. In the absence of PCE, fumarate was fermented to acetate, H(2), CO(2), and succinate. With PCE, less H(2) was formed, suggesting that PCE competed for the reducing equivalents leading to H(2). PCE dechlorination, apparently, was not outcompeted by fumarate as electron acceptor. At the optimum dissolved PCE concentration of ∼60 μM, a high dechlorination rate of 1.1 μmol h(−1) mg(−1) (dry weight) was found, which indicates that the dechlorination is not a cometabolic activity. Microscopic analysis of the fumarate-grown culture showed the dominance of a long thin rod. Molecular analysis, however, indicated the presence of two dominant species, both belonging to the 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%).