Department of Microbiology, Stellenbosch University, Private Bag X1, Matieland, 7602, South Africa.
Department of Biotechnology, University of the Western Cape, Bellville, 7535, South Africa.
Appl Microbiol Biotechnol. 2016 Sep;100(18):8241-54. doi: 10.1007/s00253-016-7735-x. Epub 2016 Jul 28.
Enzyme cost is a major impediment to second-generation (2G) cellulosic ethanol production. One strategy to reduce enzyme cost is to engineer enzyme production capacity in a fermentative microorganism to enable consolidated bio-processing (CBP). Ideally, a strain with a high secretory phenotype, high fermentative capacity as well as an innate robustness to bioethanol-specific stressors, including tolerance to products formed during pre-treatment and fermentation of lignocellulosic substrates should be used. Saccharomyces cerevisiae is a robust fermentative yeast but has limitations as a potential CBP host, such as low heterologous protein secretion titers. In this study, we evaluated natural S. cerevisiae isolate strains for superior secretion activity and other industrially relevant characteristics needed during the process of lignocellulosic ethanol production. Individual cellulases namely Saccharomycopsis fibuligera Cel3A (β-glucosidase), Talaromyces emersonii Cel7A (cellobiohydrolase), and Trichoderma reesei Cel5A (endoglucanase) were utilized as reporter proteins. Natural strain YI13 was identified to have a high secretory phenotype, demonstrating a 3.7- and 3.5-fold higher Cel7A and Cel5A activity, respectively, compared to the reference strain S288c. YI13 also demonstrated other industrially relevant characteristics such as growth vigor, high ethanol titer, multi-tolerance to high temperatures (37 and 40 °C), ethanol (10 % w/v), and towards various concentrations of a cocktail of inhibitory compounds commonly found in lignocellulose hydrolysates. This study accentuates the value of natural S. cerevisiae isolate strains to serve as potential robust and highly productive chassis organisms for CBP strain development.
酶成本是第二代（2G）纤维素乙醇生产的主要障碍。降低酶成本的一种策略是在发酵微生物中工程化酶的生产能力，以实现整合生物加工（CBP）。理想情况下，应使用具有高分泌表型、高发酵能力以及对生物乙醇特异性应激物（包括耐受预处理和木质纤维素底物发酵过程中形成的产物）固有韧性的菌株。酿酒酵母是一种稳健的发酵酵母，但作为潜在的 CBP 宿主存在一些限制，例如低异源蛋白分泌滴度。在这项研究中，我们评估了天然酿酒酵母分离株的优越分泌活性和其他在木质纤维素乙醇生产过程中所需的工业相关特性。利用天然菌株 YI13 鉴定出具有高分泌表型，与参考菌株 S288c 相比，Cel7A 和 Cel5A 的活性分别高出 3.7 倍和 3.5 倍。YI13 还表现出其他工业相关特性，例如生长活力、高乙醇浓度、对高温（37 和 40°C）、乙醇（10%w/v）和木质纤维素水解物中常见的各种抑制化合物混合物的多种耐受性。这项研究强调了天然酿酒酵母分离株的价值，可作为 CBP 菌株开发的潜在稳健和高产底盘生物。
