Recombination of the bph (Biphenyl) Catabolic Genes from Plasmid pWW100 and Their Deletion during Growth on Benzoate

ABSTRACT

Pseudomonas sp. strain CB406 was isolated from polychlorinated biphenyl-contaminated soil and harbors a nontransmissible plasmid, pWW100, of approximately 200 kb which carries the genes required for biphenyl and 4-chlorobiphenyl catabolism. The catabolic phenotype was mobilized following the construction in vivo of a cointegrate plasmid containing functional upper and lower biphenyl operons inserted into the broad-host-range R plasmid RP4. The Bph⁺ phenotype carried by pWW100 was stable in nonselective media but was unstable during growth on benzoate, where the sequential selection of two species of bph deletion derivatives occurs at high frequency. This mirrors observations made with TOL plasmids (encoding toluene and xylene catabolism) grown under similar conditions. Subcloning of dioxygenase genes involved in biphenyl catabolism confirmed the localization of the bph genes on the wild-type plasmid and the RP4 cointegrate plasmid.