Impact of oleic acid as co-substrate of glucose on "short" and "long-term" Crabtree effect in Saccharomyces cerevisiae.
BACKGROUND
Optimization of industrial biomass directed processes requires the highest biomass yield as possible. Yet, some useful yeasts like Saccharomyces cerevisiae are subject to the Crabtree effect under glucose excess. This phenomenon can occur in large scale tank where heterogeneities in glucose concentrations exist. Therefore yeasts encounter local environments with glucose excess leading to ethanol production to the detriment of biomass formation. We previously demonstrated that oleic acid as a co-substrate in glucose-limited chemostat allowed to delay and modulate the "short-term" Crabtree effect in Saccharomyces cerevisiae. Here we further investigated the effect of oleic acid as a modulator of the Crabtree effect.


RESULTS
The impact of oleic acid as co-substrate on the Crabtree effect was investigated in terms of i) strain specificity, ii) reversibility of the potential effect with aerobic glucose-excess batches and iii) durability and maximal capacities under high ethanol stress with glucose-excess fed-batches. First, the addition of oleic acid resulted in an increase of the critical dilution rate by 8% and the specific carbon uptake rate by 18%. Furthermore, a delay was observed for the onset of ethanol production when a batch was inoculated with cells previously grown in glucose-oleate chemostat. Finally, the culture of adapted cells in a glucose-oleate fed-batch led to a redirection of the carbon flux toward biomass production, with a 73% increase in the biomass yield.


CONCLUSIONS
This work demonstrated clearly that the perturbation by oleic acid as co-substrate resulted in a decrease in the "short-term" and "long-term" Crabtree effects. This impact was not strain dependent and reversible. Thus, industrial applications of this biochemical strategy could be envisaged to tackle heterogeneities issues in large scale tanks or to prepare starter yeasts for various applications.
Laboratoire d'Ingénierie des Systèmes Biologiques et des Procédés (LISBP), Institut National des Sciences Appliquées (INSA), UMR INSA/CNRS 5504, UMR INSA/INRA 792, 135 Avenue de Rangueil, 31077 Toulouse Cedex 4, France. stephane.guillouet@insa-toulouse.fr.
Jillian
J
Marc
David
D
Feria-Gervasio
Jean-Roch
JR
Mouret
Stéphane E
SE
Guillouet
D000429:Alcohol Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D005285:Fermentation; D005947:Glucose / Q000378:metabolism*; D060847:Metabolic Engineering; D019301:Oleic Acid / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*
D019301:Oleic Acid; D000429:Alcohol Oxidoreductases; C020830:glyoxylate reductase; D005947:Glucose