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Applied and Environmental Microbiology, January 2007, p. 232-242, Vol. 73, No. 1
0099-2240/07/$08.00+0     doi:10.1128/AEM.01608-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Multiple-Level Regulation of Genes for Protocatechuate Degradation in Acinetobacter baylyi Includes Cross-Regulation

Simone Yasmin Siehler, Süreyya Dal, Rita Fischer, Patricia Patz, and Ulrike Gerischer^*

Microbiology and Biotechnology, University of Ulm, Ulm, Germany

Received 12 July 2006/ Accepted 23 October 2006

The bacterium Acinetobacter baylyi uses the branched ß-ketoadipate pathway to metabolize aromatic compounds. Here, the multiple-level regulation of expression of the pca-qui operon encoding the enzymes for protocatechuate and quinate degradation was studied. It is shown that both activities of the IclR-type regulator protein PcaU at the structural gene promoter pcaIp, namely protocatechuate-dependent activation of pca-qui operon expression as well as repression in the absence of protocatechuate, can be observed in a different cellular background (Escherichia coli) and therefore are intrinsic to PcaU. The regulation of PcaU expression is demonstrated to be carbon source dependent according to the same pattern as the pca-qui operon. The increase of the pcaU gene copy number leads to a decrease of the basal expression at pcaIp, indicating that the occupancy of the PcaU binding site is well balanced and depends on the concentration of PcaU in the cell. Luciferase is used as a reporter to demonstrate strong repression of pcaIp when benzoate, a substrate of the catechol branch of the pathway, is present in addition to substrates of the protocatechuate branch (cross-regulation). The same repression pattern was observed for promoter pcaUp. Thus, three promoters involved in gene expression of enzymes of the protocatechuate branch (pobAp upstream of pobA, pcaIp, and pcaUp) are strongly repressed in the presence of benzoate. The negative effect of protocatechuate on pobA expression is not based on a direct sensing of the metabolite by PobR, the specific regulator of pobA expression.

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* Corresponding author. Mailing address: Microbiology and Biotechnology, University of Ulm, 89069 Ulm, Germany. Phone: 49-731-5022715. Fax: 49-731-5022719. E-mail: ulrike.gerischer{at}uni-ulm.de.

Published ahead of print on 3 November 2006.

Present address: Universitätsfrauenklinik und Poliklinik, University of Ulm, Ulm, Germany.

Present address: Ratiopharm GmbH, Ulm, Germany.

Present address: Lilly Deutschland GmbH, Bad Homburg, Germany.

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Applied and Environmental Microbiology, January 2007, p. 232-242, Vol. 73, No. 1
0099-2240/07/$08.00+0     doi:10.1128/AEM.01608-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

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