Function and Molecular Ecology Significance of Two Catechol-Degrading Gene Clusters in ND6.

Many bacteria metabolize aromatic compounds via catechol as a catabolic intermediate, and possess multiple genes or clusters encoding catechol-cleavage enzymes. The presence of multiple isozyme-encoding genes is a widespread phenomenon that seems to give the carrying strains a selective advantage in the natural environment over those with only a single copy. In the naphthalene-degrading strain ND6, catechol can be converted into intermediates of the tricarboxylic acid cycle via either the - or -cleavage pathways. In this study, we demonstrated that the catechol ortho-cleavage pathway genes ( and ) on the chromosome play an important role. The and operons are co-transcribed, whereas and are under independent transcriptional regulation. We examined the binding of regulatory proteins to promoters. In the presence of -muconate, a well-studied inducer of the cat gene cluster, CatR and CatR occupy an additional downstream site, designated as the activation binding site. Notably, CatR binds to both the and promoters with high affinity, while CatR binds weakly. This is likely caused by a T to G mutation in the G/T-N-A motif. Specifically, we found that CatR and CatR regulate and in a cooperative manner, which provides new insights into naphthalene degradation.