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J. Bacteriol. doi:10.1128/JB.01155-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Identification and Characterization of a Bacterial Transport System for the Uptake of Pyruvate, Propionate, and Acetate in Corynebacterium glutamicum

Institute of Biochemistry, University of Cologne, 50674 Cologne, Germany; Institute of Microbiology and Biotechnology, University of Ulm, 89069 Ulm, Germany

^* To whom correspondence should be addressed. Email: kay.marin{at}uni-koeln.de.

	Abstract

The metabolism of monocarboxylic acids is of central importance for bacteria in their natural habitat as well as during biotechnological production. Though biosynthesis and degradation is well understood, the transport of such compounds is still a matter of discussion. Here we present the identification and characterization of a new transport system in Corynebacterium glutamicum, with high affinity for acetate and propionate and with lower affinity for pyruvate. Biochemical analysis of this monocarboxylic acid transporter (MctC) revealed for the first time a quantitative discrimination of passive diffusion and active transport of acetate by bacterial cells. MctC is a secondary transporter, belongs to the class of sodium solute symporter, however, is driven by the electrochemical proton potential. The mctC gene is preceded by and co-transcribed with cg0952, a gene encoding a small membrane protein, and the transcription of the cg0952-mctC operon is under control of the transcriptional regulators RamA and RamB. Both of these proteins directly bind to the promoter region of the operon, RamA is essential for expression and RamB exerts a slightly negative control on expression of the cg0952-mctC operon. The mctC expression is induced in the presence of pyruvate and beneficial under substrate limiting conditions for C. glutamicum.