title: Metabolic flux analysis of Candida tropicalis growing on xylose in an oxygen-limited chemostat.
abstract: We have studied the metabolism of xylose by Candida tropicalis in oxygen-limited chemostat. In vitro enzyme assays indicated that glycolytic and gluconeogenetic enzymes are expressed simultaneously facilitating substrate cycling. Enhancing the redox imbalance by cofeeding of formate increased xylose and oxygen consumption rates and ethanol, xylitol, glycerol and CO2 production rates at steady state. Metabolic flux analysis (MFA) indicated that fructose 6-phosphate is replenished from the pentose phosphate pathway in sufficient amounts without contribution of the gluconeogenetic pathway. Substrate cycling between pyruvate kinase, pyruvate carboxylase and phospho-enol-pyruvate kinase increased ATP turnover. Cofeeding of formate increased the ATP yield. The ATP yields of xylose and xylose-formate cultivation were 6.9 and 8.7 mol ATP/C-mol CDW, respectively, as calculated from the MFA.
authors.affiliation: Laboratory of Bioprocess Engineering, Helsinki University of Technology, P.O.B. 6100, Kemistintie 1, FIN-02015 HUT, Finland. tom.granstrom@hut.fi
authors.forename: Tom
authors.initials: T
authors.lastname: Granström
authors.forename: Aristos A
authors.initials: AA
authors.lastname: Aristidou
authors.forename: Matti
authors.initials: M
authors.lastname: Leisola
mesh_terms: D019149:Bioreactors / Q000382:microbiology; D041022:Candida tropicalis / Q000145:classification / Q000254:growth & development* / Q000378:metabolism*; D002474:Cell-Free System; D002478:Cells, Cultured; D003198:Computer Simulation; D005561:Formates / Q000378:metabolism*; D008954:Models, Biological; D009097:Multienzyme Complexes / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D013045:Species Specificity; D015219:Substrate Cycling; D013379:Substrate Specificity; D014994:Xylose / Q000378:metabolism*
chemical_list: D005561:Formates; D009097:Multienzyme Complexes; C030544:formic acid; D014994:Xylose; D010100:Oxygen