Microbial ecology of bacterially-mediated PCB biodegradation

The roles of plamid mediated and consortia mediated polychlorinated biphenyl (PCB) biodegradation by bacterial populations isolated from PCB 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, Cl{dollar}sp-{dollar} detection, and {dollar}sp{lcub}14{rcub}{dollar}C-labeled substrate mineralization methods. A bacterial consortium, designated LPS10, involved in a concerted metabolic attack on chlorinated biphenyls, was shown to mineralize 4-chlorobiphenyl (4CB) and 4,4{dollar}spprime{dollar}-dichlorobiphenyl (4,4{dollar}spprime{dollar}CB). The LPS10 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 LPS10A which mediated the breakdown of 4CB and 4,4{dollar}spprime{dollar}CB to the putative meta-cleavage product and subsequently to 4-chlorobenzoic acid (4CBA), an isolate tentatively identified as an Arthrobacter sp. LPS10B which mediated 4CBA degradation, and Pseudomonas putida bv A LPS10C whose role in the consortium has not been determined. Bacterial isolates containing genes homologous to the plasmid pSS50, 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 degrde 4CB to 4CBA. The freshwater isolate, designated LBS1C1, 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.