Biomass Refinery Research Center, National Institute of Advanced Industrial Science and Technology, Hiroshima, Japan.
PLoS One. 2013 Jul 9;8(7):e69005. doi: 10.1371/journal.pone.0069005. Print 2013.
In the present study, comprehensive, quantitative metabolome analysis was carried out on the recombinant glucose/xylose-cofermenting S. cerevisiae strain MA-R4 during fermentation with different carbon sources, including glucose, xylose, or glucose/xylose mixtures. Capillary electrophoresis time-of-flight mass spectrometry was used to determine the intracellular pools of metabolites from the central carbon pathways, energy metabolism pathways, and the levels of twenty amino acids. When xylose instead of glucose was metabolized by MA-R4, glycolytic metabolites including 3- phosphoglycerate, 2- phosphoglycerate, phosphoenolpyruvate, and pyruvate were dramatically reduced, while conversely, most pentose phosphate pathway metabolites such as sedoheptulose 7- phosphate and ribulose 5-phosphate were greatly increased. These results suggest that the low metabolic activity of glycolysis and the pool of pentose phosphate pathway intermediates are potential limiting factors in xylose utilization. It was further demonstrated that during xylose fermentation, about half of the twenty amino acids declined, and the adenylate/guanylate energy charge was impacted due to markedly decreased adenosine triphosphate/adenosine monophosphate and guanosine triphosphate/guanosine monophosphate ratios, implying that the fermentation of xylose leads to an inefficient metabolic state where the biosynthetic capabilities and energy balance are severely impaired. In addition, fermentation with xylose alone drastically increased the level of citrate in the tricarboxylic acid cycle and increased the aromatic amino acids tryptophan and tyrosine, strongly supporting the view that carbon starvation was induced. Interestingly, fermentation with xylose alone also increased the synthesis of the polyamine spermidine and its precursor S-adenosylmethionine. Thus, differences in carbon substrates, including glucose and xylose in the fermentation medium, strongly influenced the dynamic metabolism of MA-R4. These results provide a metabolic explanation for the low ethanol productivity on xylose compared to glucose.
在本研究中，我们对重组的葡萄糖/木糖共发酵酿酒酵母 MA-R4 菌株在不同碳源（包括葡萄糖、木糖或葡萄糖/木糖混合物）发酵过程中的全面、定量代谢组进行了分析。我们使用毛细管电泳飞行时间质谱法测定了来自中心碳代谢途径、能量代谢途径和二十种氨基酸水平的细胞内代谢物库。当 MA-R4 菌株利用木糖而不是葡萄糖进行代谢时，糖酵解代谢物，包括 3-磷酸甘油酸、2-磷酸甘油酸、磷酸烯醇丙酮酸和丙酮酸，显著减少，而相反，大多数戊糖磷酸途径代谢物，如 7-磷酸景天庚酮糖和核酮糖 5-磷酸，大大增加。这些结果表明，糖酵解的低代谢活性和戊糖磷酸途径中间产物库是木糖利用的潜在限制因素。进一步证明，在木糖发酵过程中，大约一半的二十种氨基酸下降，由于三磷酸腺苷/一磷酸腺苷和三磷酸鸟苷/一磷酸鸟苷比例明显下降，腺嘌呤/鸟嘌呤能量电荷受到影响，这意味着木糖发酵导致代谢状态低效，生物合成能力和能量平衡严重受损。此外，单独用木糖发酵会大大增加三羧酸循环中柠檬酸的水平，并增加芳香族氨基酸色氨酸和酪氨酸，强烈支持诱导碳饥饿的观点。有趣的是，单独用木糖发酵也增加了多胺亚精胺及其前体 S-腺苷甲硫氨酸的合成。因此，发酵培养基中不同的碳底物（包括葡萄糖和木糖）强烈影响 MA-R4 的动态代谢。这些结果为与葡萄糖相比，木糖的乙醇生产率低提供了代谢解释。
