Karhumaa Kaisa, Garcia Sanchez Rosa, Hahn-Hägerdal Bärbel, Gorwa-Grauslund Marie-F
Department of Applied Microbiology, Lund University, P,O,Box 124, SE-22100 Lund, Sweden.
Microb Cell Fact. 2007 Feb 5;6:5. doi: 10.1186/1475-2859-6-5.
Two heterologous pathways have been used to construct recombinant xylose-fermenting Saccharomyces cerevisiae strains: i) the xylose reductase (XR) and xylitol dehydrogenase (XDH) pathway and ii) the xylose isomerase (XI) pathway. In the present study, the Pichia stipitis XR-XDH pathway and the Piromyces XI pathway were compared in an isogenic strain background, using a laboratory host strain with genetic modifications known to improve xylose fermentation (overexpressed xylulokinase, overexpressed non-oxidative pentose phosphate pathway and deletion of the aldose reductase gene GRE3). The two isogenic strains and the industrial xylose-fermenting strain TMB 3400 were studied regarding their xylose fermentation capacity in defined mineral medium and in undetoxified lignocellulosic hydrolysate.
In defined mineral medium, the xylose consumption rate, the specific ethanol productivity, and the final ethanol concentration were significantly higher in the XR- and XDH-carrying strain, whereas the highest ethanol yield was achieved with the strain carrying XI. While the laboratory strains only fermented a minor fraction of glucose in the undetoxified lignocellulose hydrolysate, the industrial strain TMB 3400 fermented nearly all the sugar available. Xylitol was formed by the XR-XDH-carrying strains only in mineral medium, whereas in lignocellulose hydrolysate no xylitol formation was detected.
Despite by-product formation, the XR-XDH xylose utilization pathway resulted in faster ethanol production than using the best presently reported XI pathway in the strain background investigated. The need for robust industrial yeast strains for fermentation of undetoxified spruce hydrolysates was also confirmed.
已使用两种异源途径构建重组木糖发酵酿酒酵母菌株：i）木糖还原酶（XR）和木糖醇脱氢酶（XDH）途径；ii）木糖异构酶（XI）途径。在本研究中，在同基因菌株背景下，使用已知可改善木糖发酵的基因修饰实验室宿主菌株（过表达木酮糖激酶、过表达非氧化戊糖磷酸途径以及缺失醛糖还原酶基因GRE3），对树干毕赤酵母XR - XDH途径和尖囊霉XI途径进行了比较。研究了这两种同基因菌株以及工业木糖发酵菌株TMB 3400在限定矿物培养基和未解毒木质纤维素水解物中的木糖发酵能力。
在限定矿物培养基中，携带XR和XDH的菌株的木糖消耗速率、比乙醇生产率和最终乙醇浓度显著更高，而携带XI的菌株乙醇产量最高。虽然实验室菌株仅发酵了未解毒木质纤维素水解物中一小部分葡萄糖，但工业菌株TMB 3400几乎发酵了所有可用糖。携带XR - XDH的菌株仅在矿物培养基中形成木糖醇，而在木质纤维素水解物中未检测到木糖醇形成。
尽管有副产物形成，但在所研究的菌株背景中，XR - XDH木糖利用途径比目前报道的最佳XI途径产生乙醇的速度更快。还证实了需要强壮的工业酵母菌株来发酵未解毒的云杉水解物。
