1-05: Gradual insight into Corynebacterium glutamicum`s central metabolism for the increase of L-lysine production

Corynebacterium glutamicum is used for the large production of amino acids like L-glutamate, L-valine or L-lysine, the latter made in a scale of 8x10⁵ annual metric tons. We applied a stoichiometric model and identified citrate synthase (CS) as most promising target to increase L-lysine production. We therefore replaced the two promoters which we identified in front of the CS gene gltA of a lysine producer by nine promoters of decreasing strength. The resulting set of strains was subsequently analysed with respect to CS activity, growth, and L-lysine yield. The decrease of CS-activity below 30% led to an increase in L-lysine yield accompanied by a decrease in growth rate. A reduced CS-activity of 6% produced an increase in L-lysine yield from 0.17 g/g to 0.32 g/g. As a further step the global consequences at the transcriptome, metabolome, and fluxome level were monitored within the strain series. Reduced CS activity results in increased expression of genes controlled by RamA and RamB, and increased cytosolic concentrations of aspartate and aspartate-derived amino acids. The fluxome study revealed that reduced CS-activity surprisingly has only a marginal influence on CS flux itself, but increases the internal concentration of oxaloacetate and acetyl-CoA ,thus showing the enormeous flexibility of C. glutamicum’s central metabolism.

This systemic approach opens an exiting new view on the system C. glutamicum as an excellent producer of bulk compounds.and sheds new light on the validity of stoichiometric models applied to the living cell.