成果報告書詳細
管理番号20090000001135
タイトル*平成20年度中間年報 新エネルギー技術研究開発/バイオマスエネルギー等高効率転換技術開発(先導技術開発)/新規エタノール発酵糸状菌を活用した稲わら等の同時糖化発酵システムの開発
公開日2010/3/10
報告書年度2008 - 2008
委託先名国立大学法人富山大学 富山県立大学
プロジェクト番号P07015
部署名新エネルギー技術開発部 バイオマスグループ
和文要約以下本編抜粋:1. 研究開発の内容及び成果等 我が国のような貧資源国では、稲わらなどのバイオマス資源を効率よくBioethanolへ変換させるための技術開発は極めて重要である。そこで、稲作から廃棄物として発生する稲わらなどからEthanolを生産する際のエネルギー投入量を軽減させることを目的として、新規な糸状菌を活用した同時糖化発酵システムを構築し、Ethanolを効率よく生産させることを検討した。平成20年度は本研究開発の下記のサブテーマを実施した。
英文要約Title: Development of Technology for High-efficiency Conversion of Biomass and Other Energy/Development of Preparatory Basic Bioenergy Technologies/Development of SSCF System to Produce Ethanol from Rice Straw Using Novel Ethanol-fermenting Fungi (FY2008-FY2009) FY2008 Annual Reports.
In a resource poor country like Japan, it is extremely important to develop new technology to efficiently convert renewable biomass into ethanol. In order to reduce the energy inputs required to efficiently produce ethanol from biomass such as rice straw generated from rice farming as agricultural residue, a simultaneous saccharification and cofermentation (SSCF) system that will use novel fungi is being constructed in this R&D project. In 2008, we investigated (1) re-screening and evaluation of characteristics of ethanol-fermenting fungi, (2) research of pathway for metabolism and fermentation of selected fungi, (3) research of hydrolases secreted by fungi, and (4) structural analysis of metabolism-related enzyme genes. A concrete content of each theme is described as follows. First, about 100 kinds of fungi (wild type: Rhizomucor genus and Mucor genus) obtained from NBRC were evaluated for the fermentation ability of pentose and hexose to ethanol. Two kinds of fungi for the efficient ethanol production were obtained (R.pusillus NBRC4578 and M.javanicas NBRC4572). Especially, it was found that M.javanicas is able to ferment various carbon sources to ethanol under an aerobic condition and to achieve the high ethanol yields on glucose and xylose (0.45 and 0.17 g-ethanol/g). Moreover, it was found that the secretion of by-products such as xylitol and glycelin was a little. As the culture condition was examined to improve the xylose fermentation performance in this strain, the ethanol yield was able to be improved to 0.26 g-ethanol/g-xylose. Furthermore, since the secretion of amylase, cellulose, and hemicellulase for degradation of rice straw etc. was verified as the secretion of the biomass hydrolases by Mucor genus were investigated, the utilization of the fungus would be expected to diminish the energy for the hydrolysis of rice straw etc. Next, the enzymes responsible for the metabolism of glucose and xylose and the ethanol fermentation were analyzed by using a biochemical technique. As a result, it was found that the fungus possess xylose reductase (XR) and xylitol dehydrogenase (XDH) for the metabolism of xylose. Its alcohol dehydrogenase (ADH) responsible for the formation of alcohol is extremely strong and further its aldehyde dehydrogenase (AlDH) to metabolize acetaldehyde oxidizing under the aerobic condition is weak. Moreover, as “Crabtree effect” was strongly expressed when the fungus metabolized pentose and/or hexose, it was suggested that in the high substrate concentration the respiratory metabolism is restrained and the metabolism was shift to ethanol fermentation side. In theme 4, the enzymes concerning the metabolism from xylose to ethanol in the ethanol-fermenting fungi, those functions at the gene level, and the structures were examined. In particular, the coenzyme specificities for XR, XDH, and ADH in R.pusillus were clarified, respectively. Especially, after the various chromatographies of the cell-free extract prepared from the fungal cultivated in broth contained xylose and its electrophoresis were carried out to purify XR and XDH, respectively, those enzymatic and chemical properties (molecular weight, subunit structure, substrate specificity etc.) were clarified. Subsequently, N-end and internal amino acid sequences of those enzymes were decided, the gene cloning were done from genome DNA based on the information, and then the primary structures were decided, respectively.
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