PCB-degrading potential of aerobic bacteria enriched from marine sediments

The main objective of this work was to study catabolic potential of marine sediment bacteria in aerobic degradation of polychlorinated biphenyls (PCBs). Marine sediment samples were collected at urban areas of the Croatian Adriatic coast, and microcosm enrichment experiments were performed in seawater mineral salts (SMS) medium with the addition of biphenyl as the only carbon source. After two to four subcultures, all enriched mixed cultures demonstrated the capability to use biphenyl, indicating that biphenyl-utilizing bacteria are widespread in coastal marine sediments. PCB-degrading activity of the enrichment cultures as well as that of their biphenyl-utilizing members were further studied in SMS medium with the addition of PCB mixtures containing di- to heptachlorinated congeners. GC–MS analyses of the extracted cultures suggested that, although they differed in PCB-degrading capabilities, all of the enrichment cultures expressed activity toward at least some of the lower chlorinated congeners (di- to tetrachlorobiphenyls). Biphenyl-utilizing bacteria isolated from the most active PCB-degrading mixed cultures showed little taxonomic diversity (six out of seven isolates belonged to the genus Rhodococcus and one to the genus Sphingomonas). All isolated Rhodococcus strains (R. erythropolis and R. ruber) showed substantial PCB-degrading activity, suggesting that these bacteria might play an important role in aerobic PCB degradation in polluted marine sediment.