Enrichment of PCB dechlorinators from sediments of the Venice lagoon

Reductive dechlorination of polychlorinated biphenyls (PCBs) has been shown to occur in contaminated marine sediments of the Venice Lagoon suspended in water coming from the same site. Aim of this work is to enrich the PCB dechlorinating population under such conditions. Native microflora was sub-cultured 5 times in the presence of exogenous PCBs (5 spiked coplanar PCBs and then Aroclor 1254) and decreasing amounts of sterile sediment. Increasing PCB-dechlorination rates were observed throughout subculturing. The culture resulting from the last transfer displayed a marked activity towards Aroclor 1254. The addition of H2 and short chain organic acids increased sulfate-reducing and methanogenic activities but did not affect the dechlorination process. However, when the same agents were applied together with vancomycin or ampicillin, remarkable and comparable increases in the dechlorination rates were detected. These findings seem to rule out sulfate-reducing and methanogenic bacteria as dechlorinators and suggest that Dehalococcoides-like bacteria, known dehalogenators resistant to the applied antibiotics, could be involved in PCB dechlorination in sediments of the Venice Lagoon.