Department of Applied Microbiology, Lund University, P,O, Box 124, S-221 00 Lund, Sweden.
Biotechnol Biofuels. 2008 Jun 11;1(1):12. doi: 10.1186/1754-6834-1-12.
Pichia stipitis xylose reductase (Ps-XR) has been used to design Saccharomyces cerevisiae strains that are able to ferment xylose. One example is the industrial S. cerevisiae xylose-consuming strain TMB3400, which was constructed by expression of P. stipitis xylose reductase and xylitol dehydrogenase and overexpression of endogenous xylulose kinase in the industrial S. cerevisiae strain USM21.
In this study, we demonstrate that strain TMB3400 not only converts xylose, but also displays higher tolerance to lignocellulosic hydrolysate during anaerobic batch fermentation as well as 3 times higher in vitro HMF and furfural reduction activity than the control strain USM21. Using laboratory strains producing various levels of Ps-XR, we confirm that Ps-XR is able to reduce HMF both in vitro and in vivo. Ps-XR overexpression increases the in vivo HMF conversion rate by approximately 20%, thereby improving yeast tolerance towards HMF. Further purification of Ps-XR shows that HMF is a substrate inhibitor of the enzyme.
We demonstrate for the first time that xylose reductase is also able to reduce the furaldehyde compounds that are present in undetoxified lignocellulosic hydrolysates. Possible implications of this newly characterized activity of Ps-XR on lignocellulosic hydrolysate fermentation are discussed.
毕赤酵母木糖还原酶（Ps-XR）已被用于设计能够发酵木糖的酿酒酵母菌株。一个例子是工业酿酒酵母木糖消耗菌株 TMB3400，它是通过在工业酿酒酵母菌株 USM21 中表达毕赤酵母木糖还原酶和木糖醇脱氢酶以及过表达内源性木酮糖激酶构建的。
在这项研究中，我们证明了菌株 TMB3400 不仅可以转化木糖，而且在厌氧分批发酵过程中对木质纤维素水解物具有更高的耐受性，以及比对照菌株 USM21 高出 3 倍的体外 HMF 和糠醛还原活性。使用产生不同水平 Ps-XR 的实验室菌株，我们证实 Ps-XR 能够在体外和体内还原 HMF。Ps-XR 的过表达使体内 HMF 转化率提高了约 20%，从而提高了酵母对 HMF 的耐受性。对 Ps-XR 的进一步纯化表明，HMF 是该酶的底物抑制剂。
我们首次证明木糖还原酶还能够还原未解毒木质纤维素水解物中存在的糠醛化合物。讨论了 Ps-XR 的这种新表征的活性对木质纤维素水解物发酵的可能影响。
