Microbial ecology of bacterially mediated PCB biodegradation

The roles of plasmid mediated and consortia mediated polychlorinated biphenyl (PCS) biodegradation by bacterial populations isolated from FOB contaminated freshwater sediments were investigated. PCB degrading bacteria were isolated by DNA;DNA colony hybridization, batch enrichments, and chemostat enrichment. Analysis of substrate removal and metabolite production were done using chlorinated biphenyl spray plates, reverse phase high pressure liquid chromatography, C1^- detection, and ¹⁴C-labeled substrate mineralization methods. A bacterial consortium, designated LPSIO, involved in a concerted metabolic attack on chlorinated biphenyls, was shown to mineralize 4-chlorobiphenyl (4CB) and 4,4'-dichlorobiphenyl (4,4'CB). The LPSIO consortium was isolated by both batch and chemostat enrichment using 4CB and biphenyl (BP) as sole carbon source and was found to have three bacterial isolates that predominated; these included; Pseudomonas testosteroni LPSlOA which mediated the breakdown of 4CB and4,4'CB to the putative meta-cleavage product and subsequently to 4-chlorobenzoic acid (4CBA), an isolate tentatively identified as an Arthrobacter sp. LPSlOB which mediated 4CBA degradation, and Pseudomonas putida bv A LPSIOC whose role in the consortium has not been determined. Bacterial isolates containing genes homologous to the plasmid pSSSO, previously characterized to mediate 4CB biodegradation. were obtained by DNA:DNA colony hybridization techniques with freshwater sediment samples and 4CB enrichments of freshwater samples. In natural sediment samples, target organisms representing 0.3% of the total population were discerned and pure cultures indicating homology to the pSS50 plasmid were shown to degrade 4CB to 4CBA. The freshwater isolate, designated LBSICI, was found to harbor the 41 Mdal plasmid pPCB that was homologous to the 35 Mdal plasmid pSS50 and this isolate was shown to mineralize 4CB. These results demonstrate that an understanding of the biodegradative capacity of individual bacterial populations as well as interacting populations of bacteria must be considered in order to gain a better understanding of the microbial ecology of PCB biodegradation.