Metabolic network analysis during fed-batch cultivation of Corynebacterium glutamicum for pantothenic acid production: first quantitative data and analysis of by-product formation
Résumé
A first generation genetically modified strain of Corynebacterium glutamicum has been assessed for its potential to synthesise and accumulate the vitamin pantothenic acid in the medium using fed-batch cultivation technology, with biomass concentration controlled by isoleucine limitation. Kinetic analysis of specific rates throughout the process has been used to model carbon flux through both central metabolism and the specific pathways involved in product formation. Flux towards pantothenic acid is potentially high but much of this flux is dissipated as by-products within associated pathways, notably linked to amino acid synthesis. The major limitation of vitamin production in this strain is linked to the tenfold higher flux of keto-isovalerate towards valine rather than pantothenic acid. Attempts to modify this ratio by imposing nitrogen limitation provoked carbon overflow as unidentified non-nitrogenous compounds. The observed accumulation of glycine suggests that the flux towards pantothenate production may by limited by the rate of the pathway intermediate (5,10-methylene-tetrahydrofolate) regeneration.