Department of Biology and Biological Engineering, Division of Industrial Biotechnology, Chalmers University of Technology, 41296, Gothenburg, Sweden.
Department of Energy, Biofuels Unit, CIEMAT, Madrid, Spain.
Appl Microbiol Biotechnol. 2019 Feb;103(3):1405-1416. doi: 10.1007/s00253-018-9528-x. Epub 2018 Nov 29.
The development of robust microorganisms that can efficiently ferment both glucose and xylose represents one of the major challenges in achieving a cost-effective lignocellulosic bioethanol production. Candida intermedia is a non-conventional, xylose-utilizing yeast species with a high-capacity xylose transport system. The natural ability of C. intermedia to produce ethanol from xylose makes it attractive as a non-GMO alternative for lignocellulosic biomass conversion in biorefineries. We have evaluated the fermentation capacity and the tolerance to lignocellulose-derived inhibitors and the end product, ethanol, of the C. intermedia strain CBS 141442 isolated from steam-exploded wheat straw hydrolysate. In a mixed sugar fermentation medium, C. intermedia CBS 141442 co-fermented glucose and xylose, although with a preference for glucose over xylose. The strain was clearly more sensitive to inhibitors and ethanol when consuming xylose than glucose. C. intermedia CBS 141442 was also subjected to evolutionary engineering with the aim of increasing its tolerance to inhibitors and ethanol, and thus improving its fermentation capacity under harsh conditions. The resulting evolved population was able to ferment a 50% (v/v) steam-exploded wheat straw hydrolysate (which was completely inhibitory to the parental strain), improving the sugar consumption and the final ethanol concentration. The evolved population also exhibited a better tolerance to ethanol when growing in a xylose medium supplemented with 35.5 g/L ethanol. These results highlight the potential of C. intermedia CBS 141442 to become a robust yeast for the conversion of lignocellulose to ethanol.
开发能够高效发酵葡萄糖和木糖的健壮微生物是实现具有成本效益的木质纤维素生物乙醇生产的主要挑战之一。中间假丝酵母（Candida intermedia）是一种非常规的木糖利用酵母，具有高容量的木糖转运系统。C. intermedia 从木糖生产乙醇的天然能力使其成为木质纤维素生物质转化为生物精炼厂中无转基因生物替代物的有吸引力的选择。我们评估了从蒸汽爆破小麦秸秆水解物中分离出的 C. intermedia 菌株 CBS 141442 的发酵能力以及对木质纤维素衍生抑制剂和终产物乙醇的耐受性。在混合糖发酵培养基中，C. intermedia CBS 141442 共发酵葡萄糖和木糖，尽管对葡萄糖的偏好高于木糖。与消耗葡萄糖相比，该菌株在消耗木糖时对抑制剂和乙醇更为敏感。C. intermedia CBS 141442 还进行了进化工程，旨在提高其对抑制剂和乙醇的耐受性，从而在恶劣条件下提高其发酵能力。由此产生的进化种群能够发酵 50%（v/v）的蒸汽爆破小麦秸秆水解物（这对亲本菌株完全具有抑制作用），提高了糖的消耗和最终乙醇浓度。在补充有 35.5 g/L 乙醇的木糖培养基中生长时，进化种群对乙醇的耐受性也更好。这些结果突出了 C. intermedia CBS 141442 成为用于将木质纤维素转化为乙醇的健壮酵母的潜力。
