Department of Microbiology, Stellenbosch University, Private Bag X1, Stellenbosch, 7602, Republic of South Africa.
Department of Process Engineering, Stellenbosch University, Private Bag X1, Stellenbosch, 7602, Republic of South Africa.
Appl Microbiol Biotechnol. 2022 Jan;106(1):455-468. doi: 10.1007/s00253-021-11710-3. Epub 2021 Dec 6.
The fermentation of spent sulphite liquor (SSL) from the pulping of hardwoods is limited by the combination of xylose, the primary fermentable sugar and high concentrations of microbial inhibitors that decrease the yeast fermentation ability. The inhibitor resistance phenotypes of xylose-capable Saccharomyces cerevisiae strains were therefore enhanced by combining rational engineering for multi-inhibitor tolerance, with adaptation in concentrated hardwood SSL as selective pressure. The adapted strains were assessed in fermentations with 60-80% v/v concentrated SSL under industrially relevant fermentation conditions. During adaptation, strains produced ethanol concentrations between 11.0 and 15.4 g/L in the range of that reported in literature. The adapted TFA40 and TP50 strains displayed enhanced inhibitor resistance phenotypes and were able to ferment xylose-rich SSL at pH below 5, exhibiting improved ethanol yields relative to the reference strain. Using yeast extract and peptone as nitrogen source in concentrated SSL fermentations further improved ethanol yields. However, strains exhibited a trade-off between resistance and ethanol productivity, indicating a carbon/energy cost for the expression of this inhibitor tolerance phenotype. KEY POINTS : • Achieved fermentation of xylose-rich hardwood spent sulphite liquor at pH below 5.0 • Adaptation of xylose-capable S. cerevisiae in concentrated spent sulphite liquor • Adapted strains exhibited enhanced inhibitor resistance phenotypes.
木质硫酸盐法制浆废蒸煮液（SSL）的发酵受到木糖（主要可发酵糖）和高浓度微生物抑制剂的限制，这些抑制剂会降低酵母的发酵能力。因此，通过将多抑制剂耐受的合理工程设计与浓缩硬木 SSL 中的适应性选择压力相结合，增强了具有木糖能力的酿酒酵母菌株的抑制剂抗性表型。在工业相关发酵条件下，用 60-80%v/v 浓缩 SSL 对适应的菌株进行发酵评估。在适应过程中，菌株在 11.0-15.4g/L 的范围内产生乙醇浓度，这与文献报道的范围相当。适应的 TFA40 和 TP50 菌株表现出增强的抑制剂抗性表型，能够在 pH 值低于 5 的富含木糖的 SSL 中发酵，与参考菌株相比，乙醇产率得到提高。在浓缩 SSL 发酵中使用酵母提取物和蛋白胨作为氮源进一步提高了乙醇产率。然而，菌株在抗性和乙醇生产力之间表现出权衡，表明这种抑制剂耐受表型的表达存在碳/能量成本。关键点：• 在 pH 值低于 5.0 的条件下实现了富含木糖的硬木硫酸盐法制浆废蒸煮液的发酵。• 在浓缩硫酸盐法制浆废水中对具有木糖能力的酿酒酵母进行了适应性驯化。• 适应的菌株表现出增强的抑制剂抗性表型。
