ABSTRACT
Previous studies have shown that Dehalococcoides species are responsible for the anaerobic bioremediation of chloroethene pollution. It has been thought that co-operation of several species is required for complete dechlorination to ethene. In the present study, we used quantitative PCR of 16 S rRNA and RDase (reductive dehalogenase) genes to examine species changes and the population of Dehalococcoides species in ground water in which the dechlorination of TCE (trichloroethene) to ethene was enhanced by delivery of hydrogen-releasing compounds. The results have shown that at least two different Dehalococcoides species co-operate in the dechlorination of TCE to ethene. Initially, the number of strains equipped with TCE RDase increased approx. 10(5)-fold. This was followed by a decrease to the original level, according to the exhaustion of TCE. Subsequently, another strain appeared, which had a VC (vinyl chloride) RDase gene similar to bvcA of Dehalococcoides sp. BAV1 and is probably responsible for the dechlorination of VC to ethene. Analysis of several genes has suggested that the former strain is like Dehalococcoides sp. FMC-TCE, and the latter strain is similar to the Dehalococcoides sp. strain that exists in the Dehalococcoides-containing mixed culture KB1. These results support the notion that monitoring Dehalococcoides species by the presence of RDase genes as genetic markers provides detailed information on the progress of bioremediation of chloroethenes, which will be useful to improve the efficiency of bioremediation.
