Cunha Joana T, Soares Pedro O, Romaní Aloia, Thevelein Johan M, Domingues Lucília
1CEB-Centre of Biological Engineering, University of Minho, 4710-057 Braga, Portugal.
2Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, Department of Biology, KU Leuven, Kasteelpark Arenberg 31, 3001 Leuven-Heverlee, Flanders Belgium.
Biotechnol Biofuels. 2019 Jan 28;12:20. doi: 10.1186/s13068-019-1360-8. eCollection 2019.
Xylose isomerase (XI) and xylose reductase/xylitol dehydrogenase (XR/XDH) pathways have been extensively used to confer xylose assimilation capacity to and tackle one of the major bottlenecks in the attainment of economically viable lignocellulosic ethanol production. Nevertheless, there is a lack of studies comparing the efficiency of those pathways both separately and combined. In this work, the XI and/or XR/XDH pathways were introduced into two robust industrial strains, evaluated in synthetic media and corn cob hemicellulosic hydrolysate and the results were correlated with the differential enzyme activities found in the xylose-pathway engineered strains.
The sole expression of XI was found to increase the fermentative capacity of both strains in synthetic media at 30 °C and 40 °C: decreasing xylitol accumulation and improving xylose consumption and ethanol production. Similar results were observed in fermentations of detoxified hydrolysate. However, in the presence of lignocellulosic-derived inhibitors, a positive synergistic effect resulted from the expression of both XI and XR/XDH, possibly caused by a cofactor equilibrium between the XDH and furan detoxifying enzymes, increasing the ethanol yield by more than 38%.
This study clearly shows an advantage of using the XI from to attain high ethanol productivities and yields from xylose. Furthermore, and for the first time, the simultaneous utilization of XR/XDH and XI pathways was compared to the single expression of XR/XDH or XI and was found to improve ethanol production from non-detoxified hemicellulosic hydrolysates. These results extend the knowledge regarding xylose assimilation metabolism and pave the way for the construction of more efficient strains for use in lignocellulosic industrial processes.
木糖异构酶（XI）途径和木糖还原酶/木糖醇脱氢酶（XR/XDH）途径已被广泛用于赋予菌株木糖同化能力，以解决木质纤维素乙醇经济可行生产中的主要瓶颈之一。然而，缺乏对这些途径单独使用和联合使用效率的比较研究。在本研究中，将XI和/或XR/XDH途径导入两种优良的工业菌株，在合成培养基和玉米芯半纤维素水解物中进行评估，并将结果与木糖途径工程菌株中发现的差异酶活性相关联。
发现单独表达XI可提高两种菌株在30°C和40°C合成培养基中的发酵能力：减少木糖醇积累，提高木糖消耗和乙醇产量。在解毒水解物发酵中也观察到类似结果。然而，在存在木质纤维素衍生抑制剂的情况下，XI和XR/XDH的表达产生了积极的协同效应，这可能是由于XDH和呋喃解毒酶之间的辅因子平衡所致，乙醇产量提高了38%以上。
本研究清楚地表明，使用来自[具体来源未提及]的XI在从木糖获得高乙醇生产率和产量方面具有优势。此外，首次将XR/XDH和XI途径的同时利用与XR/XDH或XI的单一表达进行比较，发现其可提高未解毒半纤维素水解物的乙醇产量。这些结果扩展了关于[具体微生物未提及]木糖同化代谢的知识，并为构建用于木质纤维素工业过程的更高效菌株铺平了道路。
