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A basic pattern of gene expression and of relative expression levels during different growth phases was obtained for Corynebacterium glutamicum R grown on different carbon sources. The gapA-pgk-tpi-ppc gene cluster was transcribed as a mono-or polycistronic mRNA, depending on the growth phase. The 1.4 kb (gapA) and 2.3 kb (pgk-tip) mRNAs were expressed in the early through late exponential phases, whereas the 3.7 kb (gapA-pgk-tpi) and 5.4 kb (pgk-tpi-ppc) mRNAs were only detected in the mid-exponential phase. All other glycolytic genes except pps, glk and pgi were transcribed as monocistronic mRNAs under all tested conditions. Identification and alignment of the promoter regions of the transcriptional start sites of glycolytic genes revealed strong similarities to the s A consensus promoter sequences of Gram-positive bacteria.All genes involved in glycolysis were coordinately expressed in medium containing glucose. Growth in the presence of glucose gave rise to abundant expression of most glycolytic genes, with the level of gapA transcript being the highest. Glucose depletion led to a rapid repression of most glycolytic genes and a corresponding two-to fivefold increased expression of the gluconeogenic genes pps, pck and malE, which are induced by pyruvate, lactate, acetate and/or other organic acids.

The effect of different carbon sources on the expression of tricarboxylic acid (TCA) cycle genes, along with glyoxylate bypass genes, in Corynebacterium glutamicum was determined. All TCA cycle genes were coordinately expressed in medium containing acetate. Growth in the presence of acetate gave rise to abundant expression of most TCA cycle genes, with the level of gltA transcript being the highest. However, when the cells entered the stationary phase triggered by acetate exhaustion, all genes were repressed, except sucCD and mdhB, which were slightly induced. Acetate withdrawal from the growth medium during the exponential phase also led to rapid repression of most TCA cycle genes and a corresponding twofold increase in the expression of sucCD, which were strongly induced by citrate and succinate. In addition, glucose depletion during the stationary phase led to a corresponding 8-20-fold induction of the sucCD, aceA and aceB genes. Addition of glucose to acetate medium resulted in about 10-fold induction of sucCD. The strong dependence of TCA cycle sucCD and glyoxylate bypass aceA and aceB expression on carbon source availability was confirmed and the regulatory system will be studied precisely. INTRODUCTIONCorynebacterium glutamicum, a non-pathogenic, facultative anaerobic Gram-positive soil bacterium, is widely used in the industrial production of numerous metabolites, including amino acids and organic acids (Kinoshita et al., 1957;Liebl, 2005;Nishimura et al., 2007). In contrast to closely related, medically important pathogenic species, such as Corynebacterium diphtheriae and Mycobacterium tuberculosis, C. glutamicum is generally recognized as a nonhazardous organism (Dover et al., 2004;Funke et al., 1997). Furthermore, this organism has gained increasing interest as a suitable model organism for high-G+C-content Grampositive bacteria in general and for Corynebacterineae, a suborder of the Actinomycetes, in particular.One of the central metabolic pathways in C. glutamicum and in other aerobic bacteria is the tricarboxylic acid (TCA) cycle, which is responsible for the complete oxidation of acetyl-CoA derived from various substrates and for the provision of precursors for amino acid biosynthesis. TCA cycle intermediates are commonly used by other metabolic reactions in a wide variety of cell types. Due to the commercial importance of the amino acids and organic acids produced by C. glutamicum, the control of TCA cycle enzyme activities has been the subject of intensive studies, and the phenotypes of mutants affecting TCA cycle genes have been analysed (Eikmanns et al., 1994(Eikmanns et al., , 1995Molenaar et al., 1998Molenaar et al., , 2000Usuda et al., 1996;Wittmann & De Graaf, 2005). However, limited work has been devoted to the regulation of the expression of C. glutamicum TCA cycle genes in response to different growth phases and carbon sources. Recently we have reported the transcription of C. glutamicum genes involved in the TCA cycle and glyoxylate bypass (Han et al., 2008). In fact, aspects of the re...