SUMMARY: Mixtures of 2-aminobenzenesulphonate (trivial name orthanilic acid, OA) and 3-methylbenzoic acid (3-MB), which are degraded by enzymes of plasmid-encoded pathways, can exert inhibition of growth and respiration in sp. O-1 and mt-2 depending on the ratio of their concentrations. The pronounced inhibition of sp. O-1 growing on OA by the addition of equimolar amounts of 3-MB is characterized by a rapid inactivation of the OA-converting desulphonation activity. The exconjugant sp. O/T was selected for simultaneous breakdown of OA and 3-MB by assembling the catabolic pathways from the plasmids pSAH (OA) and pWW0 (3-MB) of the above strains. The transpositional insertion of the TOL catabolic genes (Tn) from pWW0 into the recombinant plasmid of the exconjugant O/T was detected by Southern blot hybridization using the TOL plasmid as a probe. The exconjugant showed a rapid inactivation of OA desulphonation activity similar to the parent strain. However, following induction of the TOL catabolic genes and mineralization of 3-MB, the exconjugant O/T recovered and displayed high desulphonation activity, thus allowing sequential breakdown of both substrates. Our results clearly extend the expression range of the TOL catabolic genes, but not the replication ability of the plasmid, to the genus


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