Department of Microbiology, Stellenbosch University, Stellenbosch, 7602, South Africa.
Department of Biotechnology, University of Western Cape, Bellville, 7530, South Africa.
Appl Microbiol Biotechnol. 2020 Jun;104(12):5163-5184. doi: 10.1007/s00253-020-10602-2. Epub 2020 Apr 26.
Consolidated bioprocessing (CBP) of lignocellulosic material into bioethanol has progressed in the past decades; however, several challenges still exist which impede the industrial application of this technology. Identifying the challenges that exist in all unit operations is crucial and needs to be optimised, but only the barriers related to the secretion of recombinant cellulolytic enzymes in Saccharomyces cerevisiae will be addressed in this review. Fundamental principles surrounding CBP as a biomass conversion platform have been established through the successful expression of core cellulolytic enzymes, namely β-glucosidases, endoglucanases, and exoglucanases (cellobiohydrolases) in S. cerevisiae. This review will briefly address the challenges involved in the construction of an efficient cellulolytic yeast, with particular focus on the secretion efficiency of cellulases from this host. Additionally, strategies for studying enhanced cellulolytic enzyme secretion, which include both rational and reverse engineering approaches, will be discussed. One such technique includes bio-engineering within genetically diverse strains, combining the strengths of both natural strain diversity and rational strain development. Furthermore, with the advancement in next-generation sequencing, studies that utilise this method of exploiting intra-strain diversity for industrially relevant traits will be reviewed. Finally, future prospects are discussed for the creation of ideal CBP strains with high enzyme production levels.Key Points• Several challenges are involved in the construction of efficient cellulolytic yeast, in particular, the secretion efficiency of cellulases from the hosts.• Strategies for enhancing cellulolytic enzyme secretion, a core requirement for CBP host microorganism development, include both rational and reverse engineering approaches.• One such technique includes bio-engineering within genetically diverse strains, combining the strengths of both natural strain diversity and rational strain development.
木质纤维素材料的综合生物加工（CBP）转化为生物乙醇在过去几十年中取得了进展；然而，仍存在一些挑战，阻碍了该技术的工业应用。确定所有单元操作中存在的挑战至关重要，需要进行优化，但本综述仅将解决与重组纤维素酶在酿酒酵母中的分泌相关的障碍。通过成功表达核心纤维素酶，即β-葡萄糖苷酶、内切葡聚糖酶和外切葡聚糖酶（纤维二糖水解酶），已经确立了 CBP 作为生物质转化平台的基本原理。本综述将简要介绍构建高效纤维素酵母所涉及的挑战，特别关注该宿主中纤维素酶的分泌效率。此外，还将讨论研究增强纤维素酶分泌的策略，包括理性和反向工程方法。其中一种技术包括在遗传多样性菌株内进行生物工程，结合天然菌株多样性和理性菌株开发的优势。此外，随着下一代测序技术的进步，将对利用该方法开发与工业相关特性的菌株内多样性的研究进行综述。最后，讨论了创建具有高产酶水平的理想 CBP 菌株的未来前景。
