title: Metabolic fluxes in chemostat cultures of Schizosaccharomyces pombe grown on mixtures of glucose and ethanol.
abstract: Simultaneous utilization of glucose and ethanol by the yeast Schizosaccharomyces pombe CBS 356 was studied in aerobic chemostat cultures. In glucose-limited cultures, respirofermentative metabolism occurred at growth rates above 0.16 h-1. Although Sch. pombe lacks a functional glyoxylate cycle and therefore cannot utilize ethanol as a sole carbon source, ethanol was co-consumed by glucose-limited chemostat cultures. As a result, biomass yields increased, but not up to the theoretical value [0.92 g biomass (g glucose)-1] expected if all of the acetyl-CoA produced from glucose was instead synthesized from ethanol. When ethanol accounted for more than 30% of the substrate carbon in the mixed feed, it was incompletely utilized. In mixed-substrate cultures with a saturating ethanol fraction in the feed, the increase of the biomass yield as a result of ethanol consumption was highest at low dilution rates. This was not due to an increased specific rate of ethanol consumption at low growth rates; rather, the longer residence times at low dilution rates allowed Sch. pombe to utilize a larger fraction of the available ethanol, part of which was oxidized to acetate. Activities of gluconeogenic and glyoxylate-cycle enzymes were not detected in cell-free extracts of any of the cultures. Activities of acetaldehyde dehydrogenase and acetyl-CoA synthetase were low and of the same order of magnitude as the in vivo rates of acetate activation to acetyl-CoA. The results show that ethanol is a poor substrate for Sch. pombe, even as an auxiliary energy source.
authors.affiliation: Department of Microbiology and Enzymology, Kluyver Laboratory of Biotechnology, Delft University of Technology, Julianalaan 67, 2628 BC Delft, The Netherlands.
authors.forename: Patricia
authors.initials: P
authors.lastname: de Jong-Gubbels
authors.affiliation: Department of Microbiology and Enzymology, Kluyver Laboratory of Biotechnology, Delft University of Technology, Julianalaan 67, 2628 BC Delft, The Netherlands.
authors.forename: Johannes P
authors.initials: JP
authors.lastname: van Dijken
authors.affiliation: Department of Microbiology and Enzymology, Kluyver Laboratory of Biotechnology, Delft University of Technology, Julianalaan 67, 2628 BC Delft, The Netherlands.
authors.forename: Jack T
authors.initials: JT
authors.lastname: Pronk
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000332:Aerobiosis; D018533:Biomass; D004734:Energy Metabolism; D004798:Enzymes / Q000378:metabolism; D000431:Ethanol / Q000378:metabolism / Q000494:pharmacology*; D005285:Fermentation; D005656:Fungal Proteins / Q000378:metabolism; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology*; D012568:Schizosaccharomyces / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*
chemical_list: D004798:Enzymes; D005656:Fungal Proteins; D000431:Ethanol; D000255:Adenosine Triphosphate; D005947:Glucose