Department of Microbiology, University of Stellenbosch, Stellenbosch, South Africa.
Department of Biotechnology, University of Western Cape, Bellville, South Africa.
Biotechnol J. 2017 Oct;12(10). doi: 10.1002/biot.201700346. Epub 2017 Sep 15.
The yeast Saccharomyces cerevisiae has a long association with alcoholic fermentation industries and has received renewed interest as a biocatalyst for second-generation bioethanol production. Rational engineering strategies are used to create yeast strains for consolidated bioprocessing of lignocellulosic biomass. Although significant progress is made in this regard with the expression of different cellulolytic activities in yeast, cellobiohydrolase (CBH) titers remain well below ideal levels. Through classical breeding, S. cerevisiae strains with up to twofold increased CBH secretion titers is obtained in strains expressing a single gene copy. An increase of up to 3.5-fold in secreted cellobiohydrolase activity is subsequently shown for strains expressing the heterologous gene on a high copy episomal vector. To our knowledge, this is the first report of classical breeding being used to enhance heterologous protein secretion and also the most significant enhancement of CBH secretion in yeast yet reported. This enhanced secretion phenotype is specific for cellobiohydrolase I secretion, indicating that reporter protein properties might be a major determining factor for efficient protein secretion in yeast. By exploring the latent potential of different S. cerevisiae strains, the authors show that the allele pool of various strains is a valuable engineering resource to enhance secretion in yeast.
酿酒酵母与酒精发酵工业有着悠久的历史渊源，它作为第二代生物乙醇生产的生物催化剂重新受到关注。理性的工程策略被用于创造用于木质纤维素生物质的整合生物加工的酵母菌株。尽管在酵母中表达不同的纤维素酶活性方面取得了重大进展，但细胞外纤维素酶（CBH）的产量仍远低于理想水平。通过经典的选育，在表达单个基因拷贝的菌株中，获得了细胞外纤维素酶分泌产量提高了两倍的酿酒酵母菌株。随后，在表达异源基因的高拷贝附加型载体的菌株中，细胞外纤维素酶活性提高了 3.5 倍。据我们所知，这是首次报道经典选育被用于提高异源蛋白分泌，也是迄今为止报道的酿酒酵母中 CBH 分泌的最大增强。这种增强的分泌表型是细胞外纤维素酶 I 分泌的特异性，表明报告蛋白的特性可能是酵母中有效蛋白质分泌的主要决定因素。通过探索不同酿酒酵母菌株的潜在能力，作者表明，各种菌株的等位基因库是增强酵母分泌的有价值的工程资源。
