While flocculation has demonstrated its efficacy in enhancing yeast robustness and ethanol production, its potential application for lactic acid fermentation remains largely unexplored. Our study examined the differences between flocculating and nonflocculating Saccharomyces cerevisiae strains in terms of their metabolic dynamics when incorporating an exogenous lactic acid pathway, across varying cell densities and in the presence of lignocellulose-derived byproducts. Comparative gene expression profiles revealed that cultivating a nonflocculant strain at higher cell density yielded a substantial upregulation of genes associated with glycolysis, energy metabolism, and other key pathways, resulting in elevated levels of fermentation products. Meanwhile, the flocculating strain displayed an inherent ability to sustain high glycolytic activity regardless of the cell density. Moreover, our investigation revealed a significant reduction in glycolytic activity under chemical stress, potentially attributable to diminished ATP supply during the energy investment phase. Conversely, the formation of flocs in the flocculating strain conferred protection against toxic chemicals present in the medium, fostering more stable lactic acid production levels. Additionally, the distinct flocculation traits observed between the two examined strains may be attributed to variations in the nucleotide sequences of the flocculin genes and their regulators. This study uncovers the potential of flocculation for enhanced lactic acid production in yeast, offering insights into metabolic mechanisms and potential gene targets for strain improvement.

中文翻译：

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乳酸发酵中絮凝和非絮凝酵母对细胞密度和化学应激的比较反应

虽然絮凝已证明其在增强酵母稳健性和乙醇生产方面的功效，但其在乳酸发酵中的潜在应用在很大程度上仍未得到探索。我们的研究检查了絮凝和非絮凝酿酒酵母菌株在纳入外源乳酸途径、不同细胞密度和存在木质纤维素衍生副产物的情况下代谢动力学方面的差异。比较基因表达谱表明，以较高的细胞密度培养非絮凝菌株会导致与糖酵解、能量代谢和其他关键途径相关的基因大幅上调，从而导致发酵产物水平升高。同时，絮凝菌株表现出无论细胞密度如何都能维持高糖酵解活性的固有能力。此外，我们的调查显示，化学应激下糖酵解活性显着降低，这可能是由于能量投入阶段 ATP 供应减少所致。相反，絮凝菌株中絮凝物的形成可以针对培养基中存在的有毒化学物质提供保护，从而促进更稳定的乳酸生产水平。此外，在两个检查菌株之间观察到的不同絮凝特性可能归因于絮凝蛋白基因及其调节因子的核苷酸序列的变化。这项研究揭示了絮凝增强酵母乳酸产量的潜力，为代谢机制和菌株改良的潜在基因靶点提供了见解。