title: Cutting the Gordian Knot: Identifiability of anaplerotic reactions in Corynebacterium glutamicum by means of (13) C-metabolic flux analysis.
abstract: Corynebacterium glutamicum is the major workhorse for the microbial production of several amino and organic acids. As long as these derive from tricarboxylic acid cycle intermediates, the activity of anaplerotic reactions is pivotal for a high biosynthetic yield. To determine single anaplerotic activities (13) C-Metabolic Flux Analysis ((13) C-MFA) has been extensively used for C. glutamicum, however with different network topologies, inconsistent or poorly determined anaplerotic reaction rates. Therefore, in this study we set out to investigate whether a focused isotopomer model of the anaplerotic node can at all admit a unique solution for all fluxes. By analyzing different scenarios of active anaplerotic reactions, we show in full generality that for C. glutamicum only certain anaplerotic deletion mutants allow to uniquely determine the anaplerotic fluxes from (13) C-isotopomer data. We stress that the result of this analysis for different assumptions on active enzymes is directly transferable to other compartment-free organisms. Our results demonstrate that there exist biologically relevant metabolic network topologies for which the flux distribution cannot be inferred by classical (13) C-MFA.
authors.affiliation: Institute of Bio- and Geosciences, IBG-1:Biotechnology, Forschungszentrum Jülich, D-52425, Jülich, Germany.
authors.forename: Jannick
authors.initials: J
authors.lastname: Kappelmann
authors.affiliation: Institute of Bio- and Geosciences, IBG-1:Biotechnology, Forschungszentrum Jülich, D-52425, Jülich, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wiechert
authors.affiliation: Institute of Bio- and Geosciences, IBG-1:Biotechnology, Forschungszentrum Jülich, D-52425, Jülich, Germany. s.noack@fz-juelich.de.
authors.forename: Stephan
authors.initials: S
authors.lastname: Noack
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D002247:Carbon Isotopes / Q000378:metabolism*; D002264:Carboxylic Acids / Q000378:metabolism*; D048230:Corynebacterium glutamicum / Q000378:metabolism*; D064688:Metabolic Flux Analysis; D053858:Metabolic Networks and Pathways
chemical_list: D000596:Amino Acids; D002247:Carbon Isotopes; D002264:Carboxylic Acids
keywords: 13C-metabolic flux analysis; C. glutamicum; anaplerosis; flux observability; metabolic fluxes; structural identifiability