title: Intracellular carbon fluxes in riboflavin-producing Bacillus subtilis during growth on two-carbon substrate mixtures.
abstract: Metabolic responses to cofeeding of different carbon substrates in carbon-limited chemostat cultures were investigated with riboflavin-producing Bacillus subtilis. Relative to the carbon content (or energy content) of the substrates, the biomass yield was lower in all cofeeding experiments than with glucose alone. The riboflavin yield, in contrast, was significantly increased in the acetoin- and gluconate-cofed cultures. In these two scenarios, unusually high intracellular ATP-to-ADP ratios correlated with improved riboflavin yields. Nuclear magnetic resonance spectra recorded with amino acids obtained from biosynthetically directed fractional (13)C labeling experiments were used in an isotope isomer balancing framework to estimate intracellular carbon fluxes. The glycolysis-to-pentose phosphate (PP) pathway split ratio was almost invariant at about 80% in all experiments, a result that was particularly surprising for the cosubstrate gluconate, which feeds directly into the PP pathway. The in vivo activities of the tricarboxylic acid cycle, in contrast, varied more than twofold. The malic enzyme was active with acetate, gluconate, or acetoin cofeeding but not with citrate cofeeding or with glucose alone. The in vivo activity of the gluconeogenic phosphoenolpyruvate carboxykinase was found to be relatively high in all experiments, with the sole exception of the gluconate-cofed culture.
authors.affiliation: Institute of Biotechnology, ETH Zürich, CH-8093 Zürich, Switzerland.
authors.forename: Michael
authors.initials: M
authors.lastname: Dauner
authors.forename: Marco
authors.initials: M
authors.lastname: Sonderegger
authors.forename: Michel
authors.initials: M
authors.lastname: Hochuli
authors.forename: Thomas
authors.initials: T
authors.lastname: Szyperski
authors.forename: Kurt
authors.initials: K
authors.lastname: Wüthrich
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Hohmann
authors.forename: Uwe
authors.initials: U
authors.lastname: Sauer
authors.forename: James E
authors.initials: JE
authors.lastname: Bailey
mesh_terms: D001412:Bacillus subtilis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D018533:Biomass; D050260:Carbohydrate Metabolism; D002244:Carbon / Q000378:metabolism*; D002247:Carbon Isotopes / Q000378:metabolism; D003470:Culture Media; D005942:Gluconates; D009682:Magnetic Resonance Spectroscopy; D012256:Riboflavin / Q000096:biosynthesis*
chemical_list: D002247:Carbon Isotopes; D003470:Culture Media; D005942:Gluconates; D002244:Carbon; C030691:gluconic acid; D012256:Riboflavin