Xylose is the most prevalent sugar available in hemicellulose fraction of lignocellulosic biomass (LCB) and of great interest for the green economy. Unfortunately, most of the cell factories cannot inherently metabolize xylose as sole carbon source. Yarrowia lipolytica is a non-conventional yeast that produces industrially important metabolites. The yeast is able to metabolize a large variety of substrates including both hydrophilic and hydrophobic carbon sources. However, Y. lipolytica lacks effective metabolic pathway for xylose uptake and only scarce information is available on utilization of xylose. For the economica feasibility of LCB-based biorefineries, effective utilization of both pentose and hexose sugars is obligatory. In the present study, succinic acid (SA) production from xylose by Y. lipolytica was examined. To this end, Y. lipolytica PSA02004 strain was engineered by overexpressing pentose pathway cassette comprising xylose reductase (XR), xylitol dehydrogenase (XDH) and xylulose kinase (XK) gene. The recombinant strain exhibited a robust growth on xylose as sole carbon source and produced substantial amount of SA. The inhibition of cell growth and SA formation was observed above 60 g/L xylose concentration. The batch cultivation of the recombinant strain in a bioreactor resulted in a maximum biomass concentration of 7.3 g/L and SA titer of 11.2 g/L with the yield of 0.19 g/g. Similar results in terms of cell growth and SA production were obtained with xylose-rich hydrolysate derived from sugarcane bagasse. The fed-batch fermentation yielded biomass concentration of 11.8 g/L (OD600: 56.1) and SA titer of 22.3 g/L with a gradual decrease in pH below 4.0. Acetic acid was obtained as a main by-product in all the fermentations. The recombinant strain displayed potential for bioconversion of xylose to SA. Further, this study provided a new insight on conversion of lignocellulosic biomass into value-added products. To the best of our knowledge, this is the first study on SA production by Y. lipolytica using xylose as a sole carbon source.

中文翻译：

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通过工程解脂耶氏酵母从木糖生物生产琥珀酸，无需 pH 控制。


木糖是木质纤维素生物质 (LCB) 半纤维素部分中最常见的糖，对绿色经济具有极大的意义。不幸的是，大多数细胞工厂本身不能将木糖作为唯一碳源进行代谢。解脂耶氏酵母是一种非常规酵母，可产生工业上重要的代谢物。酵母能够代谢多种底物，包括亲水性和疏水性碳源。然而，解脂耶氏酵母缺乏有效的木糖摄取代谢途径，并且关于木糖利用的信息很少。为了实现基于 LCB 的生物精炼厂的经济可行性，必须有效利用戊糖和己糖。在本研究中，研究了解脂耶氏酵母从木糖生产琥珀酸（SA）的情况。为此，通过过表达包含木糖还原酶(XR)、木糖醇脱氢酶(XDH)和木酮糖激酶(XK)基因的戊糖途径盒来工程化解脂耶氏酵母PSA02004菌株。该重组菌株以木糖作为唯一碳源表现出强劲的生长并产生大量的SA。木糖浓度高于 60 g/L 时观察到细胞生长和 SA 形成的抑制。重组菌株在生物反应器中分批培养，最大生物量浓度为7.3 g/L，SA效价为11.2 g/L，产量为0.19 g/g。使用源自甘蔗渣的富含木糖的水解产物在细胞生长和 SA 生产方面获得了类似的结果。补料分批发酵产生的生物量浓度为 11.8 g/L (OD600: 56.1)，SA 滴度为 22.3 g/L，pH 逐渐降低至 4.0 以下。乙酸是所有发酵过程中的主要副产物。 重组菌株显示出木糖生物转化为SA的潜力。此外，这项研究还为将木质纤维素生物质转化为增值产品提供了新的见解。据我们所知，这是首次对解脂耶氏酵母使用木糖作为唯一碳源生产SA的研究。