Characterization of the microbial community from the marine sediment of the Venice lagoon capable of reductive dechlorination of coplanar polychlorinated biphenyls (PCBs)

The native microbial community of a contaminated sediment from Brentella Canal (Venice Lagoon, Italy) was enriched in slurry microcosms consisting of sterile sediment suspended in sterile site water in the presence of 3,3′,4,4′-tetrachlorobiphenyl, 3,3′,4,4′,5- and 2,3′,4,4′,5-pentachlorobiphenyls, 3,3′,4,4′,5,5′- and 2,3,3′,4,4′,5-hexachlorobiphenyls. The enrichment cultures were characterized at each subculturing step by 16S rRNA gene Terminal-Restriction Fragment Length Polymorphism (T-RFLP) and Denaturing Gradient Gel Electrophoresis (DGGE) analysis. About 90% of spiked polychlorinated biphenyls (PCBs) were stoichiometrically converted into di- and tri-chlorinated congeners by each enriched culture via dechlorination of flanked para chlorines and ortho-flanked meta chlorines. A 2-fold increase in PCB-dechlorination rate, the disappearance of lag phase, as well as a remarkable increase of sulfate consumption and a decline of methanogenic activity, were observed throughout subculturing. A reduction of complexity of the archaeal community, which was composed by Methanomicrobiales and Methanosarcinales, was also observed as a result of culture enrichment. The bacterial community included members of the Alpha, Gamma, Delta and Epsilon divisions of Proteobacteria, Firmicutes and Chloroflexi. Two sequence phylotypes related to the genus Sulforovum and the species Desulfococcus multivorans and two Chloroflexi enriched throughout subculturing, thus suggesting that these bacteria were involved in PCB dechlorination in the marine sediments of Brentella canal.