Catabolic plasmid specifying polychlorinated biphenyl degradation in Cupriavidus sp. strain SK-4: Mobilization and expression in a pseudomonad

Strain SK-4, a polychlorinated biphenyl (PCB) degrader previously reported to utilize di-ortho-substituted biphenyl, was genotypically re-characterized as a species of Cupriavidus. The bacterium harbored a single plasmid (pSK4), which resisted curing and which, after genetic marking by a transposon (SK4Tn5), could be mobilized into a pseudomonad. Analysis of pSK4 in both the transconjugant and the wild type revealed that it specifies the genes coding for 2-hydroxy-2,4-pentadienoate degradation in addition to those of the upper biphenyl pathway. Expression of the benzoate metabolic pathway in the transconjugant is evidence suggesting that the benzoate catabolic genes are also localized on the plasmid. This implies that pSK4 codes for all the genes involved in biphenyl mineralization. It is therefore reasonable to propose that the plasmid is the determinant for the unique metabolic capabilities known to exist in Cupriavidus sp. strain SK-4.