Utilization of phenoxyacetic acid, by strains using either the ortho or meta cleavage of catechol during phenol degradation, after conjugal transfer of tfdA, the gene encoding a 2,4-dichlorophenoxyacetic acid/2-oxoglutarate dioxygenase

The degradation of recalcitrant pollutants in contaminated soils and waters could be facilitated by broadening the degradative capabilities of indigen ous microbes by the conjugal transfer of catabolic genes. The feasibility o f establishing bacterial populations that degrade phenoxyacetic acid by con jugal transfer of tfdA, the gene encoding 2,4-dichlorophenoxyacetic acid/2- oxoglutarate dioxygenase, to phenol-degrading strains of Pseudomonas and Ra lstonia was examined. The mobilizable plasmid pKJS32 served as a vector for delivery of tfdA and the regulatory gene, tfdS. Transconjugant strains tha t degraded phenol by an ortho cleavage of catechol grew well on phenoxyacet ic acid while those employing a meta cleavage could only grow on phenoxyace tic acid in the presence of benzoic acid or after a prolonged lag period an d the appearance of mutants that had gained catechol 1,2-dioxygenase activi ties. Thus, an ortho cleavage of catechol was essential for degradation of phenoxyacetic acid, suggesting that a product of the or tho-cleavage pathwa y, probably cis,cis-muconic acid, is an inducer of tfdA gene expression. Es tablishment of phenoxyacetic-acid-degrading soil populations by conjugal tr ansfer of tfdA would depend on the presence of phenol-degrading recipients employing an ol tho cleavage of catechol.