In vivo reactivation of catechol 2,3-dioxygenase mediated by a chloroplast-type ferredoxin: a bacterial strategy to expand the substrate specificity of aromatic degradative pathways

The meta-cleavage operon of the TOL plasmid pWW0 of Pseudomonas putida contains 13 genes responsible for the oxidation of benzoate and toluates to Krebs cycle intermediates via estradiol (meta) cleavage of (methyl)catechol. The functions of all the genes are known with the exception of xylT. We constructed pWW0 mutants defective in the xylT gene, and found that these mutants were not able to grow on p-toluate while they were still capable of growing on benzoate and m-toluate. In the xylT mutants, all the meta-cleavage enzymes were induced by p-toluate with the exception of catechol 2,3-dioxygenase whose activity was 1% of the p-toluate-induced activity in wild-type cells. Addition of 4-methylcatechol to m-toluate-grown wild-type and xylT cells resulted in the inactivation of catechol 2,3-dioxygenase in these cells. In the wild-type strain but not in the xylT mutant, the catechol 2,3-dioxygenase activity was regenerated in a short time. The regeneration of the catechol 2,3-dioxygenase activity was also observed in H2O2-treated wild-type cells, but not in H2O2-treated xylT cells. We concluded that the xylT product is required for the regeneration of catechol 2,3-dioxygenase.