COMETABOLIC OXIDATION OF POLYCHLORINATED-BIPHENYLS IN SOIL WITH A SURFACTANT-BASED FIELD APPLICATION VECTOR

Polychlorinated biphenyl (PCB)-degradative genes, under the control of a constitutive promoter, were cloned into a broad-host-range plasmid and a transposon. These constructs were inserted into a surfactant-uti lizing strain, Pseudomonas putida IPL5, to create a field application vector (FAV) in which a surfactant-degrading organism cometabolizes PC B. By utilizing a surfactant not readily available to indigenous popul ations and a constitutive promoter, selective growth and PCB degradati ve gene expression are decoupled from biphenyl. Since PCB degradation via the biphenyl degradation pathway is nonadaptive in the absence of biphenyl, there is no selective pressure for PCB gene maintenance. The recombinant strains exhibited degradative activity against 25 of 33 P CB congeners in Aroclor 1248 in the absence of biphenyl. Whole-cell en zyme assays indicated that PCB-degradative activity of a recombinant s train carrying the PCB genes on a plasmid was approximately twice that of the same strain carrying the PCB genes on a transposon. Plasmid lo ss rates in the absence of antibiotic selection averaged 7.4% per cell division and were highly variable between experiments. Surfactant-ame nded slurries of PCB-contaminated electric power plant substation soil were inoculated with approximately 10(5) recombinant cells per ml. Th e populations of the added strains increased to greater than 10(9) cel ls per ml in 2 days, and cell growth coincided,vith PCB degradation. B y 15 days, 50 to 60% of the indicator congener 2,3,2',5'-tetrachlorobi phenyl was degraded. The effectiveness of PCB degradation by the plasm id-containing strain depended on plasmid stability. The transposon enc oded PCB genes were much more stable, and in surfactant-amended soil s lurries, PCB degradation was more consistent between experiments.