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Journal of Bacteriology, February 2007, p. 1055-1060, Vol. 189, No. 3
0021-9193/07/$08.00+0     doi:10.1128/JB.01467-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Cyclohexa-1,5-Diene-1-Carbonyl-Coenzyme A (CoA) Hydratases of Geobacter metallireducens and Syntrophus aciditrophicus: Evidence for a Common Benzoyl-CoA Degradation Pathway in Facultative and Strict Anaerobes{triangledown}

Franziska Peters,1 Yoshifumi Shinoda,1 Michael J. McInerney,2 and Matthias Boll3*

Institute for Biology II, Microbiology, University of Freiburg, 79104 Freiburg, Germany,1 Department of Botany and Microbiology, University of Oklahoma, Norman, Oklahoma 73019,2 Institute of Biochemistry, University of Leipzig, 04103 Leipzig, Germany3

Received 17 September 2006/ Accepted 13 November 2006

In the denitrifying bacterium Thauera aromatica, the central intermediate of anaerobic aromatic metabolism, benzoyl-coenzyme A (CoA), is dearomatized by the ATP-dependent benzoyl-CoA reductase to cyclohexa-1,5-diene-1-carbonyl-CoA (dienoyl-CoA). The dienoyl-CoA is further metabolized by a series of ß-oxidation-like reactions of the so-called benzoyl-CoA degradation pathway resulting in ring cleavage. Recently, evidence was obtained that obligately anaerobic bacteria that use aromatic growth substrates do not contain an ATP-dependent benzoyl-CoA reductase. In these bacteria, the reactions involved in dearomatization and cleavage of the aromatic ring have not been shown, so far. In this work, a characteristic enzymatic step of the benzoyl-CoA pathway in obligate anaerobes was demonstrated and characterized. Dienoyl-CoA hydratase activities were determined in extracts of Geobacter metallireducens (iron reducing), Syntrophus aciditrophicus (fermenting), and Desulfococcus multivorans (sulfate reducing) cells grown with benzoate. The benzoate-induced genes putatively coding for the dienoyl-CoA hydratases in the benzoate degraders G. metallireducens and S. aciditrophicus were heterologously expressed and characterized. Both gene products specifically catalyzed the reversible hydration of dienoyl-CoA to 6-hydroxycyclohexenoyl-CoA (Km, 80 and 35 µM; Vmax, 350 and 550 µmol min–1 mg–1, respectively). Neither enzyme had significant activity with cyclohex-1-ene-1-carbonyl-CoA or crotonyl-CoA. The results suggest that benzoyl-CoA degradation proceeds via dienoyl-CoA and 6-hydroxycyclohexanoyl-CoA in strictly anaerobic bacteria. The steps involved in dienoyl-CoA metabolism appear identical in all nonphotosynthetic anaerobic bacteria, although totally different benzene ring-dearomatizing enzymes are present in facultative and obligate anaerobes.


* Corresponding author. Mailiing address: Institute for Biochemistry, Brüderstr. 34, D-04103 Leipzig, Germany. Phone: 49-341-9736996. Fax: 49-341-9736919. E-mail: boll{at}uni-leipzig.de.

{triangledown} Published ahead of print on 22 November 2006.


Journal of Bacteriology, February 2007, p. 1055-1060, Vol. 189, No. 3
0021-9193/07/$08.00+0     doi:10.1128/JB.01467-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.




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