Raghavendran Vijayendran, Marx Christian, Olsson Lisbeth, Bettiga Maurizio
Department of Biology and Biological Engineering, Chalmers University of Technology, Kemivägen 10, 412 96, Göteborg, Sweden.
Faculty of Sciences I-Biosciences, Institute of Pharmacy, Department of Pharmaceutical Technology and Biopharmacy, Martin-Luther-Universität Halle-Wittenberg, Weinbergweg 22, 06120, Halle (Saale), Germany.
AMB Express. 2020 Dec 17;10(1):219. doi: 10.1186/s13568-020-01148-7.
To enhance the competitiveness of industrial lignocellulose ethanol production, robust enzymes and cell factories are vital. Lignocellulose derived streams contain a cocktail of inhibitors that drain the cell of its redox power and ATP, leading to a decrease in overall ethanol productivity. Many studies have attempted to address this issue, and we have shown that increasing the glutathione (GSH) content in yeasts confers tolerance towards lignocellulose inhibitors, subsequently increasing the ethanol titres. However, GSH levels in yeast are limited by feedback inhibition of GSH biosynthesis. Multidomain and dual functional enzymes exist in several bacterial genera and they catalyse the GSH biosynthesis in a single step without the feedback inhibition. To test if even higher intracellular glutathione levels could be achieved and if this might lead to increased tolerance, we overexpressed the genes from two bacterial genera and assessed the recombinants in simultaneous saccharification and fermentation (SSF) with steam pretreated spruce hydrolysate containing 10% solids. Although overexpressing the heterologous genes led to a sixfold increase in maximum glutathione content (18 µmol g) compared to the control strain, this only led to a threefold increase in final ethanol titres (8.5 g L). As our work does not conclusively indicate the cause-effect of increased GSH levels towards ethanol titres, we cautiously conclude that there is a limit to cellular fitness that could be accomplished via increased levels of glutathione.
为提高工业木质纤维素乙醇生产的竞争力，强大的酶和细胞工厂至关重要。木质纤维素衍生的物流含有多种抑制剂，这些抑制剂会耗尽细胞的氧化还原能力和三磷酸腺苷（ATP），导致乙醇总体生产率下降。许多研究试图解决这个问题，我们已经表明，提高酵母中的谷胱甘肽（GSH）含量可赋予对木质纤维素抑制剂的耐受性，进而提高乙醇产量。然而，酵母中的GSH水平受到GSH生物合成反馈抑制的限制。多结构域和双功能酶存在于几个细菌属中，它们可在一步中催化GSH生物合成而无反馈抑制。为了测试是否可以实现更高的细胞内谷胱甘肽水平以及这是否可能导致耐受性增加，我们过表达了来自两个细菌属的基因，并在含有10%固体的蒸汽预处理云杉水解物的同步糖化发酵（SSF）中评估了重组体。尽管过表达异源基因导致最大谷胱甘肽含量（18 μmol g）相比对照菌株增加了六倍，但这仅导致最终乙醇产量增加了三倍（8.5 g L）。由于我们的工作并未确凿表明GSH水平增加对乙醇产量的因果关系，我们谨慎地得出结论，通过增加谷胱甘肽水平来实现细胞适应性存在一定限度。
