Harner Nicole K, Wen Xin, Bajwa Paramjit K, Austin Glen D, Ho Chi-Yip, Habash Marc B, Trevors Jack T, Lee Hung
School of Environmental Sciences, University of Guelph, Guelph, ON, N1G 2W1, Canada.
J Ind Microbiol Biotechnol. 2015 Jan;42(1):1-20. doi: 10.1007/s10295-014-1535-z. Epub 2014 Nov 18.
Lignocellulosic substrates are the largest source of fermentable sugars for bioconversion to fuel ethanol and other valuable compounds. To improve the economics of biomass conversion, it is essential that all sugars in potential hydrolysates be converted efficiently into the desired product(s). While hexoses are fermented into ethanol and some high-value chemicals, the bioconversion of pentoses in hydrolysates remains inefficient. This remains one of the key challenges in lignocellulosic biomass conversion. Native pentose-fermenting yeasts can ferment both glucose and xylose in lignocellulosic biomass to ethanol. However, they perform poorly in the presence of hydrolysate inhibitors, exhibit low ethanol tolerance and glucose repression, and ferment pentoses less efficiently than the main hexoses glucose and mannose. This paper reviews classical and molecular strain improvement strategies applied to native pentose-fermenting yeasts for improved ethanol production from xylose and lignocellulosic substrates. We focus on Pachysolen tannophilus, Scheffersomyces (Candida) shehatae, Scheffersomyces (Pichia) stipitis, and Spathaspora passalidarum which are good ethanol producers among the native xylose-fermenting yeasts. Strains obtained thus far are not robust enough for efficient ethanol production from lignocellulosic hydrolysates and can benefit from further improvements.
木质纤维素底物是用于生物转化为燃料乙醇和其他有价值化合物的可发酵糖的最大来源。为了提高生物质转化的经济性，至关重要的是将潜在水解产物中的所有糖高效转化为所需产物。虽然己糖可发酵生成乙醇和一些高价值化学品，但水解产物中戊糖的生物转化效率仍然较低。这仍然是木质纤维素生物质转化中的关键挑战之一。天然的戊糖发酵酵母可以将木质纤维素生物质中的葡萄糖和木糖都发酵成乙醇。然而，它们在水解产物抑制剂存在的情况下表现不佳，乙醇耐受性低且存在葡萄糖阻遏现象，并且发酵戊糖的效率低于主要的己糖葡萄糖和甘露糖。本文综述了应用于天然戊糖发酵酵母的经典和分子菌株改良策略，以提高从木糖和木质纤维素底物生产乙醇的效率。我们重点关注嗜鞣管囊酵母、树干毕赤酵母、树干毕赤酵母和嗜木生斯巴假丝酵母，它们是天然木糖发酵酵母中良好的乙醇生产者。迄今为止获得的菌株对于从木质纤维素水解产物高效生产乙醇来说还不够强健，需要进一步改良。
