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.
Microb Cell Fact. 2013 Sep 23;12:83. doi: 10.1186/1475-2859-12-83.
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.
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.
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.
优化工业生物质定向过程需要尽可能高的生物质产量。然而，一些有用的酵母，如酿酒酵母，在葡萄糖过剩时会受到 Crabtree 效应的影响。这种现象可能会在存在葡萄糖浓度不均匀的大型罐中发生。因此，酵母会遇到局部葡萄糖过剩的环境，导致乙醇的产生，而不利于生物质的形成。我们之前证明，在葡萄糖限制的恒化器中，作为共底物的油酸可以延迟和调节酿酒酵母中的“短期”Crabtree 效应。在这里，我们进一步研究了油酸作为 Crabtree 效应调节剂的作用。
从以下几个方面研究了油酸作为共底物对 Crabtree 效应的影响：i）菌株特异性，ii）有氧葡萄糖过量批次中潜在效应的可逆性，以及 iii）高乙醇胁迫下葡萄糖过量 fed-batch 中的耐用性和最大容量。首先，油酸的添加使临界稀释率增加了 8%，比碳摄取率增加了 18%。此外，当用先前在葡萄糖-油酸恒化器中生长的细胞接种分批培养时，观察到乙醇产生的起始延迟。最后，在葡萄糖-油酸 fed-batch 中培养适应细胞导致碳通量向生物质生产的重新定向，生物质产率增加了 73%。
这项工作清楚地表明，油酸作为共底物的扰动导致“短期”和“长期”Crabtree 效应的降低。这种影响与菌株无关且可逆。因此，这种生化策略的工业应用可以用来解决大型罐中的不均匀性问题，或为各种应用准备起始酵母。
