Design of a Saccharomyces cerevisiae strain capable of simultaneously utilizing cellobiose and xylose

Saccharomyces cerevisiae;bioethanol production;cellobiose assimilation;aldose 1-epimerase

Li, Sijin ; Zhao ; Huimin

关键词: Saccharomyces cerevisiae;    bioethanol production;    cellobiose assimilation;    aldose 1-epimerase;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/45696/Sijin_Li.pdf?sequence=3&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Saccharomyces cerevisiae has been widely utilized as a platform microorganism forbioethanol production from lignocelluloses. However, glucose repression limits efficientethanol production because glucose in lignocellulosic hydrolysates inhibits xylose and othersugars’ utilization. As a result, it is attractive to construct a glucose derepressed S. cerevisiaestrain for efficient utilization of lignocellulosic sugars.In this thesis, we proposed and constructed an artificial cellobiose assimilatingpathway consisting of a cellobiose transporter and a β-glucosidase in S. cerevisiae. A total ofsix different cellobiose assimilating pathways were constructed and compared in a laboratoryS. cerevisiae strain capable of xylose utilization and the one with best fermentationperformance was selected. The resultant yeast strain showed significantly improvedcellobiose and xylose consumption ability and ethanol productivity in both shake-flask andbioreactor fermentation. The xylose consumption rate was enhanced by 42% to 0.68 g L-1 h-1in the engineered laboratory strain, and a maximum ethanol productivity of 0.49 g L-1 h-1wasobtained, with no obvious glucose repression phenomenon observed. The maximum ethanolyield achieved was 0.39 g per g sugar. In addition, the best cellobiose assimilating pathwaywas also transferred to an industrial yeast strain and the resultant industrial strain showedgreatly improved fermentation performance. The ethanol productivity was 0.64 g L-1 h-1, theethanol yield was 0.42 g per g sugar, and the cellobiose consumption rate was more than 1.77g L-1 h-1, which enables fast and efficient ethanol production from lignocelluloses. Thus thisapproach has been demonstrated to be a promising method to overcome glucose repressionand at the same time enhance ethanol productivity.iiiIt was found that a small amount of glucose was accumulated during either cellobiosefermentation or cellobiose and xylose co-fermentation, which inevitably decreased theethanol yield and productivity. To address this limitation, the role of mutarotase, also calledaldose 1-epimerase, which is capable of converting glucose between two anomers wasinvestigated. Three endogenous mutarotase genesYHR210c, YNR071c and GAL10 wereidentified in S. cerevisiae s288c wild type strain. The natural cellobiose assimilating strainNeurospora crassa also has a mutarotase gene named NCU09705. Overexpression of bothS. cerevisiae and N. crassa aldose 1-epimerases showed improved sugar consumption andethanol production in cellobiose assimilating S. cerevisiae strains and aldose 1-epimerasedisrupted S. cerevisiae strains derived from the s288c strain showed significant drawbacks incellobiose utilization.