Journal of Bacteriology, September 1998, p. 4466-4474, Vol. 180, No. 17
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Department of Microbiology, University of Georgia, Athens, Georgia 30602-2605
Received 4 May 1998/Accepted 18 June 1998
Acinetobacter sp. strain ADP1 can use benzoate or
anthranilate as a sole carbon source. These structurally
similar compounds are independently converted to catechol, allowing
further degradation to proceed via the
-ketoadipate pathway. In
this study, the first step in anthranilate catabolism was
characterized. A mutant unable to grow on
anthranilate, ACN26, was selected. The sequence of a
wild-type DNA fragment that restored growth revealed the
antABC genes, encoding 54-, 19-, and 39-kDa proteins,
respectively. The deduced AntABC sequences were homologous to those of
class IB multicomponent aromatic ring-dihydroxylating enzymes,
including the dioxygenase that initiates benzoate catabolism.
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 dioxygenase
(AntABC) catalyzed catechol formation without requiring a
dehydrogenase. In Acinetobacter mutants,
benC substituted for antC during growth on
anthranilate, suggesting relatively broad substrate
specificity of the BenC reductase, which transfers electrons from NADH
to the terminal oxygenase. In contrast, the benAB genes did
not substitute for antAB. An antA point
mutation in ACN26 prevented anthranilate degradation, and
this mutation was independent of a mucK mutation in the
same strain that prevented exogenous muconate degradation.
Anthranilate induced expression of antA, although
no associated transcriptional regulators were identified. Disruption of three open reading frames in the immediate vicinity of
antABC did not prevent the use of
anthranilate as a sole carbon source. The
antABC genes were mapped on the ADP1 chromosome and were not linked to the two known supraoperonic gene clusters involved in aromatic compound degradation.
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