Enrichment and characterization of a PCB dechlorinating community in a contaminated sediment of Venice lagoon

A PCB dechlorinating community occurring in a contaminated sediment of the Venice lagoon was enriched and characterized under slurry-phase anaerobic conditions by using sterile sediment and water coming from the site in the presence of 5 spiked coplanar PCB congeners at 500 mg/kg. In the primary microcosm, the dechlorination activity started after a five-month lag phase, after which all spiked PCBs were markedly transformed into lower chlorinated congeners with a dechlorination rate of 112±26 Cl/kg of sediment/week. No lag phase and significantly higher dechlorination rates, as well as a marked increase in sulfate-reduction and a progressive decrease in the methanogenic activity, were detected after serial transfers of the culture. Consistently, T-RFLP analysis of 16S rDNA showed a progressive reduction in the complexity of the archaeal community and an enrichment of several eubacterial taxons during the culture transfer process. Preliminary cloning and sequencing operations indicate that sulfate-reducing bacteria are among the forms mostly enriched in the last enrichment culture. This suggests that such a group of bacteria contributes to the PCB dechlorination activity detected.