Comamonas testosteroni YZW-D was isolated from Passaic River sediment for its ability to degrade isophthalate and terephthalate. Degradation of the two isomeric compounds proceeds via separately inducible catabolic pathways that converge at protocatechuate. Analysis of the catabolic pathways by which these two isomers are degraded demonstrated that a cis-dihydrodiol intermediate is involved in both pathways. The genes for the conversion of isophthalate and terephthalate to protocatechuate were cloned on a single fragment of genomic DNA from C. testosteroni YZW-D. The two operons were located by subcloning and mutant complementation experiments. The regions coding for the two degradative pathways were sequenced. Analysis of the nucleotide sequence for the isophthalate degradation operon located genes for a dioxygenase, a transport protein, a cis-dihydrodiol dehydrogenase, and a reductase. Analysis of the nucleotide sequence for the terephthalate degradation operon located genes for a regulatory protein, a transport protein, a dioxygenase large subunit, a dioxygenase small subunit, a cis-dihydrodiol dehydrogenase, and a reductase.