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PhD student Yusuke Sasaki
Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Japan
Title of the talk: Xylose Fermentation of Xylose Isomerase-Displaying Yeast
To realize efficient bioethanol production from non-edible biomass using Saccharomyces cerevisiae, xylan utilization is essential. Although xylan-assimilating yeasts were even constructed, the efficiency of the ethanol production remains trivial principally due to bottlenecks in both of a saccharification and a fermentation step.
Here, we engineered a novel xylan-degrading strain that co-displays an endo-1,4-β-xylanase (Xyn11B derived from Saccharophagus degradans) and a β-xylosidase (XlnD derived from Aspergillus niger) tethered to the cell surface of S. cerevisiae through the cell wall anchoring protein, α-agglutinin1. The constructed yeast successfully degraded xylan and produced d-xylose, which was confirmed using HPLC and DNS assay.
Also, an advanced yeast strain displaying xylose isomerase (XylC) derived from Clostridium cellulovorans2 on the cell surface was constructed to ferment d-xylose. Xylose isomerase naturally requires a metal cation as its cofactor, whereas the specified cation of XylC has never been examined. Therefore, we identified a divalent cobalt cation as the most preferable cofactor, and found that the cation dramatically developed the enzymatic activity. Based on this result, we further improved the xylose consumption and ethanol production rate by utilizing the divalent cobalt cation. To achieve direct ethanol production from xylan, we constructed a novel and unique co-culture system consisting both of the xylan-degrading and d-xylose-assimilating yeast strains. Results represented that the co-culture system achieved high ethanol yield from xylan3.
Y. Sasaki is the candidate PhD at Graduate School of Advanced Integrated Studies in Human Survivability, Kyoto University. He has already submitted papers of the first author in journals and has the experience of presentation twice at the international congress; Pacifichem 2015 and ECB 2016.