Institute of Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, 845 38 Bratislava, Slovak Republic.
Department of Applied Biotechnology and Food Science, Budapest University of Technology and Economics, 1111 Budapest, Hungary.
Biotechnol Adv. 2022 Oct;59:107981. doi: 10.1016/j.biotechadv.2022.107981. Epub 2022 May 14.
Microbes and their carbohydrate-active enzymes are central for depolymerization of complex lignocellulosic polysaccharides in the global carbon cycle. Their unique abilities to degrade and ferment carbohydrates are also utilized in many industrial processes such as baking, brewing and production of biofuels and drugs. Effective degradation and utilization of cellulose and hemicelluloses is important for the shift towards green bioeconomy, and requires microbes equipped with proper sets of carbohydrate-active enzymes (CAZymes). Knowledge of cellulolytic and xylanolytic CAZymes has mainly been generated from bacteria and filamentous fungi, while yeasts have been largely overlooked and may represent an untapped resource in natural CAZymes with industrial relevance. Cellulose and xylan-degrading yeasts with the ability to ferment saccharides are also promising candidates for consolidated bioprocesses (CBPs), as they can degrade lignocellulose and utilize its constituents to produce desired products at the same time. Cellulolytic yeasts able to utilize insoluble crystalline cellulose are rare while xylanolytic yeasts are rather widespread in nature. The lack of particular enzymes in yeasts can be remediated by introducing the missing enzymes into strains having outstanding product-forming attributes. In this review, we provide a comprehensive overview of the cellulose- and xylan-degrading ascomycetous and basidiomycetous yeasts known to date. We describe how these yeasts can be identified through bioprospecting and bioinformatic approaches and summarize available growth and enzymatic assays for strain characterization. Known and predicted CAZymes are extensively analyzed, both in individual species and in a phylogenetic perspective. We also describe the strategies used for construction of recombinant cellulolytic and xylanolytic strains as well as current applications for polysaccharide-degrading yeasts. Finally, we discuss the great potential of these yeasts as industrial cell factories, identify open research questions and provide suggestions for future investigations.
微生物及其碳水化合物活性酶是全球碳循环中复杂木质纤维素多糖解聚的核心。它们降解和发酵碳水化合物的独特能力也被广泛应用于许多工业过程，如烘焙、酿造以及生物燃料和药物的生产。有效降解和利用纤维素和半纤维素对于向绿色生物经济转变至关重要，这需要微生物配备适当的碳水化合物活性酶（CAZymes）。对纤维素酶和木聚糖酶的了解主要来自于细菌和丝状真菌，而酵母在很大程度上被忽视了，它们可能代表着具有工业相关性的天然 CAZymes 中的未开发资源。具有降解纤维素和木聚糖能力并能发酵糖的纤维素和木聚糖降解酵母也是整合生物加工（CBPs）的有前途的候选者，因为它们可以降解木质纤维素并同时利用其成分生产所需的产品。能够利用不溶性结晶纤维素的纤维素降解酵母很少，而木聚糖降解酵母在自然界中则相当广泛。酵母中缺乏特定的酶可以通过将缺失的酶引入具有出色产品形成特性的菌株中来修复。在本综述中，我们全面概述了迄今为止已知的具有降解纤维素和木聚糖能力的子囊菌和担子菌酵母。我们描述了如何通过生物勘探和生物信息学方法来识别这些酵母，并总结了用于菌株表征的现有生长和酶测定方法。已知和预测的 CAZymes 都进行了广泛分析，无论是在单个物种还是在系统发育视角下。我们还描述了构建重组纤维素和木聚糖降解菌株的策略以及多糖降解酵母的当前应用。最后，我们讨论了这些酵母作为工业细胞工厂的巨大潜力，确定了开放的研究问题，并为未来的研究提供了建议。
