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Microbiology 155 (2009), 3632-3640; DOI  10.1099/mic.0.031401-0
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Microbiology 155 (2009), 3632-3640; DOI  10.1099/mic.0.031401-0
© 2009 Society for General Microbiology

Regulation of tartrate metabolism by TtdR and relation to the DcuS–DcuR-regulated C4-dicarboxylate metabolism of Escherichia coli

Ok Bin Kim{dagger}, Julia Reimann, Hanna Lukas, Uwe Schumacher, Jan Grimpo, Pia Dünnwald and Gottfried Unden

Institut für Mikrobiologie und Weinforschung, Johannes Gutenberg-Universität Mainz, Becherweg 15, 55099 Mainz, Germany

Escherichia coli catabolizes L-tartrate under anaerobic conditions to oxaloacetate by the use of L-tartrate/succinate antiporter TtdT and L-tartrate dehydratase TtdAB. Subsequently, L-malate is channelled into fumarate respiration and degraded to succinate by the use of fumarase FumB and fumarate reductase FrdABCD. The genes encoding the latter pathway (dcuB, fumB and frdABCD) are transcriptionally activated by the DcuS–DcuR two-component system. Expression of the L-tartrate-specific ttdABT operon encoding TtdAB and TtdT was stimulated by the LysR-type gene regulator TtdR in the presence of L- and meso-tartrate, and repressed by O2 and nitrate. Anaerobic expression required a functional fnr gene, and nitrate repression depended on NarL and NarP. Expression of ttdR, encoding TtdR, was repressed by O2, nitrate and glucose, and positively regulated by TtdR and DcuS. Purified TtdR specifically bound to the ttdR–ttdA promoter region. TtdR was also required for full expression of the DcuS–DcuR-dependent dcuB gene in the presence of tartrate. Overall, expression of the ttdABT genes is subject to L-/meso-tartrate-dependent induction, and to aerobic and nitrate repression. The control is exerted directly at ttdA and in addition indirectly by regulating TtdR levels. TtdR recognizes a subgroup (L- and meso-tartrate) of the stimuli perceived by the sensor DcuS, which responds to all C4-dicarboxylates; both systems apparently communicate by mutual regulation of the regulatory genes.

Correspondence
Gottfried Unden
unden{at}uni-mainz.de

Abbreviations: FNR, fumarate nitrate reductase regulator

{dagger}Present address: Department of Life Sciences, Ewha Womans University, Seoul, Republic of Korea.






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