Growth of Corynebacterium glutamicum on fructose was significantly less than that obtained on glucose, despite similar rates of substrate uptake. This was in part due to the production of overflow metabolites (dihydroxyacetone and lactate) but also to the increased production of CO 2 during growth on fructose. These differences in carbon-metabolite accumulation are indicative of a different pattern of carbon-flux distribution through the central metabolic pathways. Growth on glucose has been previously shown to involve a high flux (Ͼ 50% of total glucose consumption) via the pentose pathway to generate anabolic reducing equivalents. NMR analysis of carbon-isotope distribution patterns of the glutamate pool after growth on 1-13 C-or 6- 13C-enriched fructose indicates that the contribution of the pentose pathway is significantly diminished during exponential growth on fructose with glycolysis being the predominant pathway (80 % of total fructose consumption). The increased flux through glycolysis during growth on fructose is associated with an increased NADH/NAD ϩ ratio susceptible to inhibit both glyceraldehyde-3-phosphate dehydrogenase and pyruvate dehydrogenase, and provoking the overflow of metabolites derived from the substrates of these two enzymes. The biomass yield observed experimentally is higher than can be estimated from the apparent quantity of NADPH associated with the pentose pathway and the flux through isocitrate dehydrogenase, suggesting an additional reaction yielding NADPH. This may involve a modified tricarboxylic acid cycle involving malic enzyme, expressed to significantly higher levels during growth on fructose than on glucose, and a pyruvate carboxylating anaplerotic enzyme.Keywords : Corynebacterium glutamicum; fructose metabolism; NMR analysis; NADH/NAD ϩ ratio; overflow metabolism.For several decades, Corynebacterium glutamicum and re-as to more efficiently supply the specific biosynthetic pathways with the necessary carbon precursors and coenzymes. lated species have been exploited industrially for the production of various amino acids. Improvements of the fermentation strateAlthough many enzymes of intermediary metabolism have been isolated from Brevibacterium flavum and characterised pregies employed and of the bacterial strains by genetic engineering techniques have been achieved, leading to progressively increas-dominantly by the team of Shiio [5Ϫ7], global carbon-flux models based on regulatory or energetic principles have only reing rates of production and/or yields [1]. These strategies have often been based upon overcoming the natural feedback regula-ceived attention recently. Over the last five years, various groups have examined how glucose is catabolised by the central pathtion mechanisms specific to each biosynthetic pathway [2Ϫ4] and have enabled a detailed understanding of these biochemical ways using NMR [8Ϫ10], enzymatic [11] and mathematical modelling [12,13] approaches. A general consensus opinion has sequences to be established. It is now apparent that further impr...

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Malic enzyme is one of at least five enzymes, known to be present in Corynebacterium glutamicum, capable of carboxylation and decarboxylation reactions coupling glycolysis and the tricarboxylic acid cycle. To date, no information is available concerning the physiological role of the malic enzyme in this bacterium. The malE gene from C. glutamicum has been cloned and sequenced. The protein encoded by this gene has been purified to homogeneity, and the biochemical properties have been established. Biochemical characteristics indicate a decarboxylation role linked to NADPH generation. Strains of C. glutamicum in which the malE gene had been disrupted or overexpressed showed no detectable phenotype during growth on either acetate or glucose, but showed a significant modification of growth behavior during lactate metabolism. The wild type showed a characteristic brief period of exponential growth on lactate followed by a linear growth period. This growth pattern was further accentuated in a malE-disrupted strain (⌬malE). However, the strain overexpressing malE maintained exponential growth until all lactate had been consumed. This strain accumulated significantly larger amounts of pyruvate in the medium than the other strains.