Biology Department, Central Michigan University, Mt Pleasant, MI 48859, USA.
Biotechnol Biofuels. 2010 Jan 15;3:2. doi: 10.1186/1754-6834-3-2.
Biofuels offer a viable alternative to petroleum-based fuel. However, current methods are not sufficient and the technology required in order to use lignocellulosic biomass as a fermentation substrate faces several challenges. One challenge is the need for a robust fermentative microorganism that can tolerate the inhibitors present during lignocellulosic fermentation. These inhibitors include the furan aldehyde, furfural, which is released as a byproduct of pentose dehydration during the weak acid pretreatment of lignocellulose. In order to survive in the presence of furfural, yeast cells need not only to reduce furfural to the less toxic furan methanol, but also to protect themselves and repair any damage caused by the furfural. Since furfural tolerance in yeast requires a functional pentose phosphate pathway (PPP), and the PPP is associated with reactive oxygen species (ROS) tolerance, we decided to investigate whether or not furfural induces ROS and its related cellular damage in yeast.
We demonstrated that furfural induces the accumulation of ROS in Saccharomyces cerevisiae. In addition, furfural was shown to cause cellular damage that is consistent with ROS accumulation in cells which includes damage to mitochondria and vacuole membranes, the actin cytoskeleton and nuclear chromatin. The furfural-induced damage is less severe when yeast are grown in a furfural concentration (25 mM) that allows for eventual growth after an extended lag compared to a concentration of furfural (50 mM) that prevents growth.
These data suggest that when yeast cells encounter the inhibitor furfural, they not only need to reduce furfural into furan methanol but also to protect themselves from the cellular effects of furfural and repair any damage caused. The reduced cellular damage seen at 25 mM furfural compared to 50 mM furfural may be linked to the observation that at 25 mM furfural yeast were able to exit the furfural-induced lag phase and resume growth. Understanding the cellular effects of furfural will help direct future strain development to engineer strains capable of tolerating or remediating ROS and the effects of ROS.
生物燃料为石油基燃料提供了一种可行的替代品。然而，目前的方法还不够完善，而将木质纤维素生物质作为发酵基质所需的技术则面临着诸多挑战。其中一个挑战是需要一种能够耐受木质纤维素发酵过程中存在的抑制剂的强壮发酵微生物。这些抑制剂包括糠醛醛，糠醛是木质纤维素在弱酸预处理过程中戊糖脱水的副产物。为了在糠醛存在的情况下存活，酵母细胞不仅需要将糠醛还原为毒性较小的呋喃甲醇，还需要保护自身并修复糠醛造成的任何损伤。由于酵母的糠醛耐受性需要功能性戊糖磷酸途径（PPP），而 PPP 与活性氧物种（ROS）耐受性相关，因此我们决定研究糠醛是否会在酵母中诱导 ROS 及其相关的细胞损伤。
我们证明糠醛会诱导酿酒酵母中 ROS 的积累。此外，糠醛还会导致细胞损伤，这与细胞中 ROS 积累一致，包括线粒体和液泡膜、肌动蛋白细胞骨架和核染色质的损伤。与阻止生长的 50mM 糠醛浓度相比，当酵母在允许在延长的迟滞期后最终生长的 25mM 糠醛浓度下生长时，糠醛诱导的损伤较轻。
这些数据表明，当酵母细胞遇到抑制剂糠醛时，它们不仅需要将糠醛还原为呋喃甲醇，还需要保护自身免受糠醛的细胞影响并修复任何造成的损伤。与在 50mM 糠醛浓度下阻止生长相比，在 25mM 糠醛浓度下观察到的细胞损伤较小，这可能与在 25mM 糠醛浓度下酵母能够退出糠醛诱导的迟滞期并恢复生长的观察结果有关。了解糠醛的细胞效应将有助于指导未来的菌株开发，以工程化能够耐受或修复 ROS 和 ROS 效应的菌株。
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