Concurrent hexachlorobenzene and chloroethene transformation by endogenous dechlorinating microorganisms in the Ebro River sediment

The ability of Dehalococcoides spp. to reduce chlorinated compounds offers a great potential for bioremediation and/or bioaugmentation of contaminated environments. So far, however, our knowledge of the activity of Dehalococcoides spp. in situ is limited to only a few subsurface environments. The aim of this study was to broaden this knowledge to other environments, and we investigated the role of Dehalococcoides spp. in the transformation of chlorinated benzenes and chlorinated ethenes in the Ebro River (Spain) sediments. Lab-scale batch microcosms were used to follow the growth and abundance of Dehalococcoides spp. during the transformation of selected chlorinated compounds. We applied biomolecular tools targeting the 16S rRNA, the 16S rRNA gene and several functional genes involved in dechlorination in combination with chemical measurements. The growth of Dehalococcoides spp. and the differential expression of several reductive dehalogenase genes during the dechlorination process could be demonstrated. Furthermore, 16S rRNA gene-based clone libraries of dechlorinating river sediment showed a complex community structure and indicated the involvement of several additional bacterial genera in the transformation process, underlining the remarkable potential of this rivers' sediment to transform different halo-organic pollutants.