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 tolua tes to Krebs cycle intermediates via extradiol (meta) cleavage of (met hyl)catechol. The functions of all the genes are known with the except ion of xylT. We constructed pWW0 mutants defective in the xylT gene, a nd found that these mutants were not able to grow on p-toluate while t hey were still capable of growing on benzoate and m-toluate. In the xy lT mutants, all the meta-cleavage enzymes were induced by p-toluate wi th the exception of catechol 2,3-dioxygenase whose activity was 1% of the p-toluate-induced activity in wild-type cells. Addition of 4-methy lcatechol to m-toluate-grown wild-type and xylT cells resulted in the inactivation of catechol 2,3-dioxygenase in these cells. In the wild-t ype strain but not in the xylT mutant, the catechol 2,3-dioxygenase ac tivity was regenerated in a short time. The regeneration of the catech ol 2,3-dioxygenase activity was also observed in H2O2-treated wild-typ e cells, but not in H2O2-treated xylT cells. We concluded that the xyl T product is required for the regeneration of catechol 2,3-dioxygenase .