微生物細胞表面工程是利用細胞表面表現技術，使外源蛋白固定化於細胞表面，可應用於細胞催化反應、細胞吸附劑、活疫苗、生物感測器等領域。本研究探討將來自Bacillus circulans subsp. Alkalophilus之Beta-葡萄糖苷酵素(Beta-glucosidase)表現於酵母菌細胞表面，達到酵素固定化之目的，並應用於纖維素之水解發酵生產生質酒精(bioethanol)。Beta-葡萄糖苷酵素(Beta-glucosidase)可將纖維雙醣(cellobiose)水解成葡萄糖，提供給酵母菌生長及產生酒精，本論文所建構之表面表現質體pYDAGA2-Bgl轉入酵母菌宿主細胞中經誘導後，可將100 g/l之纖維雙醣(cellobiose)轉化產生出約23 g/l之酒精，而宿主細胞本身則無法利用纖維雙糖產出酒精，此能在表面表現Beta-glucosidase之酵母菌將有利於直接利用纖維素同步醣化發酵(SSF)產生酒精。由於一般商業纖維素水解酵素中較缺乏Beta-葡萄糖苷酵素(Beta-glucosidase)，在水解纖維素的過程中會導致Endo-1,4-Beta-D-glucanase 及Exo-1,4-Beta-D-glucanase 之酵素活性會受到纖維雙醣(cellobiose)之抑制，而利用酵母菌細胞表面表現Beta-葡萄糖苷酵素(Beta-glucosidase)可填補商業酵素中此酵素之不足，實驗結果顯示轉型菌株SC-pYDAGA2-Bgl生產3g/l之酒精約只需要6hr，而宿主細胞需花約30hr，成功提升利用纖維素同步糖化發酵生產酒精之效率。

The engineering of cell surface display is immobilization of heterogeneous protein on cell surface . It is widely used in catalytic reaction of cell , adsorbent of cell , vaccine , biosensor .We discuss that we will display Beta-glucosidase on yeast surface and use it to produce bioethanol from cellulose.Beta-glucosidase can hydrolyzes cellobiose to glucose that can provide energy for biomass and producing ethanol. 100(g/l) cellobiose as carbon source can obtain 23(g/l) ethanol from Beta-glucosidase-surface displaying yeast , but host can’t produce any ethanol , therefore the technology is opportunity to directly utilize cellulose to produce ethanol by simultaneous saccharification and fermentation (SSF) . Although commercial cellulose from Trichoderma contain endogenous Beta-glucosidase , but the activities of this enzyme are generally insufficient to prevent the accumulation of cellobiose, resulting in product inhibition of endoglucanases and cellobiohydrolases. Therefore we tried genetically to immobilize Beta-glucosidase on the cell surface of the yeast Saccharomyces cerevisiae in its active form to supply this insufficient enzyme , and then successfully promote the efficiency of producing ethanol from cellulose by SSF process .

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