Persson Viktor C, Perruca Foncillas Raquel, Anderes Tegan R, Ginestet Clément, Gorwa-Grauslund Marie
Division of Applied Microbiology, Department of Chemistry, Lund University, Lund, Sweden.
Biotechnol Biofuels Bioprod. 2023 Nov 6;16(1):168. doi: 10.1186/s13068-023-02422-z.
Over the last decades, many strategies to procure and improve xylose consumption in Saccharomyces cerevisiae have been reported. This includes the introduction of efficient xylose-assimilating enzymes, the improvement of xylose transport, or the alteration of the sugar signaling response. However, different strain backgrounds are often used, making it difficult to determine if the findings are transferrable both to other xylose-consuming strains and to other xylose-assimilation pathways. For example, the influence of anomerization rates between α- and β-xylopyranose in pathway optimization and sugar sensing is relatively unexplored.
In this study, we tested the effect of expressing a xylose epimerase in S. cerevisiae strains carrying different xylose-consuming routes. First, XIs originating from three different species in isogenic S. cerevisiae strains were tested and the XI from Lachnoclostridium phytofermentans was found to give the best performance. The benefit of increasing the anomerization rate of xylose by adding a xylose epimerase to the XI strains was confirmed, as higher biomass formation and faster xylose consumption were obtained. However, the impact of xylose epimerase was XI-dependent, indicating that anomer preference may differ from enzyme to enzyme. The addition of the xylose epimerase in xylose reductase/xylitol dehydrogenase (XR/XDH)-carrying strains gave no improvement in xylose assimilation, suggesting that the XR from Spathaspora passalidarum had no anomer preference, in contrast to other reported XRs. The reduction in accumulated xylitol that was observed when the xylose epimerase was added may be associated with the upregulation of genes encoding endogenous aldose reductases which could be affected by the anomerization rate. Finally, xylose epimerase addition did not affect the sugar signaling, whereas the type of xylose pathway (XI vs. XR/XDH) did.
Although xylose anomer specificity is often overlooked, the addition of xylose epimerase should be considered as a key engineering step, especially when using the best-performing XI enzyme from L. phytofermentans. Additional research into the binding mechanism of xylose is needed to elucidate the enzyme-specific effect and decrease in xylitol accumulation. Finally, the differences in sugar signaling responses between XI and XR/XDH strains indicate that either the redox balance or the growth rate impacts the SNF1/Mig1p sensing pathway.
在过去几十年中，已报道了许多在酿酒酵母中获取和改善木糖消耗的策略。这包括引入高效的木糖同化酶、改善木糖转运或改变糖信号响应。然而，经常使用不同的菌株背景，这使得难以确定这些发现是否可转移到其他消耗木糖的菌株以及其他木糖同化途径。例如，在途径优化和糖感知中，α-和β-吡喃木糖之间的异头物异构化速率的影响相对未被探索。
在本研究中，我们测试了在携带不同木糖消耗途径的酿酒酵母菌株中表达木糖差向异构酶的效果。首先，测试了源自同基因酿酒酵母菌株中三个不同物种的木糖异构酶（XIs），发现来自植物发酵产琥珀酸丝状杆菌的XI表现最佳。通过向XI菌株中添加木糖差向异构酶来提高木糖的异头物异构化速率的益处得到了证实，因为获得了更高的生物量形成和更快的木糖消耗。然而，木糖差向异构酶的影响依赖于XI，这表明不同酶的异头物偏好可能不同。在携带木糖还原酶/木糖醇脱氢酶（XR/XDH）的菌株中添加木糖差向异构酶并没有改善木糖同化，这表明与其他报道的XRs相比，来自巴氏嗜热孢霉的XR没有异头物偏好。添加木糖差向异构酶时观察到的积累木糖醇的减少可能与编码内源性醛糖还原酶的基因上调有关，而这些基因可能受异头物异构化速率影响。最后，添加木糖差向异构酶不影响糖信号，而木糖途径的类型（XI与XR/XDH）则有影响。
尽管木糖异头物特异性常常被忽视，但添加木糖差向异构酶应被视为关键的工程步骤，特别是当使用来自植物发酵产琥珀酸丝状杆菌的性能最佳的XI酶时。需要对木糖的结合机制进行更多研究，以阐明酶特异性效应和木糖醇积累的减少。最后，XI和XR/XDH菌株之间糖信号响应的差异表明，氧化还原平衡或生长速率会影响SNF1/Mig1p传感途径。
