Direct production of bioethanol from Jerusalem artichoke inulin by gene-engineering Saccharomyces cerevisiae 6525 with exoinulinase gene

Jerusalem artichoke( Helianthustuberosus L.), an important crop, containing over 50% inulinin its tubers on a dry weight basis is an agricultural and industrial cropwith a great potential for production of ethanol and industrial products. Inulinis a good substrate for bioethanol production. Saccharomyces cerevisiae 6525 can produce high concentrations of ethanol, but it cannot synthesize inulinase. In this study, a new integration vector carrying inuA1 gene encoding exoinulinase was constructed and transformed into 18SrDNA site of industrial strain S. cerevisiae 6525. The obtained transformant, BR8, produced 1.1UmL(-1) inulinaseactivity within 72h and the dry cellweight reached 12.3gL(-1) within 48h. In a small-scale fermentation, BR8 produced 9.5% (v/v) ethanol, with a productivity rate of 0.385g ethanol per gram inulin, while wild-type S. cerevisiae 6525 produced only 3.3% (v/v) ethanol in the same conditions. In a 5-L fermentation, BR8 produced 14.0% (v/v) ethanol in fermentation medium containing inulinand 1% (w/v) (NH4)(2)SO4. The engineered S. cerevisiae 6525 carrying inuA1 converted pure nonhydrolyzed inulindirectly into high concentrations of ethanol.