Role of “Dehalococcoides” spp. in the Anaerobic Transformation of Hexachlorobenzene in European Rivers
ABSTRACTThe diffuse pollution by chlorinated organic compounds in river basins is a concern, due to their potential adverse effects on human health and the environment. Organohalides, like hexachlorobenzene (HCB), are recalcitrant to aerobic microbial degradation, and “Dehalococcoides” spp. are the only known microorganisms capable of anaerobic transformation of these compounds coupled to their growth. In this study, sediments from four European rivers were studied in order to determine their HCB dechlorination capacities and the role ofDehalococcoidesspp. in this process. Only a weak correlation was observed betweenDehalococcoidesspecies abundance and HCB transformation rates from different locations. In one of these locations, in the Ebro River sediment, HCB dechlorination could be linked toDehalococcoidesspecies growth and activity by 16S rRNA-based molecular methods. Furthermore, HCB dechlorination activity in this sediment was found over the full range of ambient temperatures that this sediment can be exposed to during different seasons throughout the year. The sediment contained several reductive dehalogenase (rdh) genes, and analysis of their transcription revealed the dominance ofcbrA, previously shown to encode a trichlorobenzene reductive dehalogenase. This study investigated the role ofDehalococcoidesspp. in HCB dechlorination in river sediments and evaluated if the current knowledge ofrdhgenes could be used to assess HCB bioremediation potential.