SIMILARITIES BETWEEN THE ANTABC-ENCODED ANTHRANILATE DIOXYGENASE AND THE BENABC-ENCODED BENZOATE DIOXYGENASE OF ACINETOBACTER SP. STRAIN ADP1

Acinetobacter sp, strain ADP1 can use benzoate or anthranilate as a so le carbon source. These structurally similar compounds are independent ly converted to catechol, allowing further degradation to proceed via the beta-ketoadipate pathway, In this study, the first step in anthran ilate catabolism was characterized, A mutant unable to grow on anthran ilate, ACN26, was selected. The sequence of a wild-type DNA fragment t hat restored growth revealed the antABC genes, encoding 54-, 19-, and 39-kDa proteins, respectively. The deduced AntABC sequences were homol ogous to those of class IB multicomponent aromatic ring-dihydroxylatin g enzymes, including the dioxygenase that initiates benzoate catabolis m. Expression of antABC in Escherichia coli, a bacterium that normally does not degrade anthranilate, enabled the conversion of anthranilate to catechol, Unlike benzoate dioxygenase (BenABC), anthranilate dioxy genase (AntABC) catalyzed catechol formation without requiring a dehyd rogenase. In Acinetobacter mutants, benC substituted for antC during g rowth on anthranilate, suggesting relatively broad substrate specifici ty of the BenC reductase, which transfers electrons from NADH to the t erminal oxygenase, In contrast, the benAB genes did not substitute for antAB. An antA point mutation in ACN26 prevented anthranilate degrada tion, and this mutation was independent of a mucK mutation in the same strain that prevented exogenous muconate degradation. Anthranilate in duced expression of antA, although no associated transcriptional regul ators were identified, Disruption of three open reading frames in the immediate vicinity of antABC did not prevent the use of anthranilate a s a sole carbon source. The antABC genes were mapped on the ADP1 chrom osome and were not linked to the two known supraoperonic gene clusters involved in aromatic compound degradation.