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Journal of Bacteriology, March 2008, p. 1620-1630, Vol. 190, No. 5
0021-9193/08/$08.00+0     doi:10.1128/JB.01221-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Anaerobic Metabolism of Catechol by the Denitrifying Bacterium Thauera aromatica—a Result of Promiscuous Enzymes and Regulators?

Mikrobiologie, Fakultät für Biologie, Universität Freiburg, Freiburg, Germany

Received 29 July 2007/ Accepted 10 December 2007

The anaerobic metabolism of catechol (1,2-dihydroxybenzene) was studied in the betaproteobacterium Thauera aromatica that was grown with CO₂ as a cosubstrate and nitrate as an electron acceptor. Based on different lines of evidence and on our knowledge of enzymes and genes involved in the anaerobic metabolism of other aromatic substrates, the following pathway is proposed. Catechol is converted to catechylphosphate by phenylphosphate synthase, which is followed by carboxylation by phenylphosphate carboxylase at the para position to the phosphorylated phenolic hydroxyl group. The product, protocatechuate (3,4-dihydroxybenzoate), is converted to its coenzyme A (CoA) thioester by 3-hydroxybenzoate-CoA ligase. Protocatechuyl-CoA is reductively dehydroxylated to 3-hydroxybenzoyl-CoA, possibly by 4-hydroxybenzoyl-CoA reductase. 3-Hydroxybenzoyl-CoA is further metabolized by reduction of the aromatic ring catalyzed by an ATP-driven benzoyl-CoA reductase. Hence, the promiscuity of several enzymes and regulatory proteins may be sufficient to create the catechol pathway that is made up of elements of phenol, 3-hydroxybenzoate, 4-hydroxybenzoate, and benzoate metabolism.

Published ahead of print on 21 December 2007.