Ethanol production from Jerusalem artichoke tubers at high temperature by newly isolated thermotolerant inulin-utilizing yeast Kluyveromyces marxianus using consolidated bioprocessing

Abstract

Thermotolerant inulin-utilizing yeast strains were successfully isolated in this study. Among the isolated strains, Kluyveromyces marxianus DBKKU Y-102 was found to be the most effective strain for direct ethanol fermentation at high temperature from fresh Jerusalem artichoke (JA) tubers without inulin hydrolysis under consolidated bioprocessing (CBP). The maximum ethanol concentrations produced by this strain under the optimum culture conditions were 104.83 and 97.46 g L(-1) at 37 and 40 °C, respectively. Data from this study clearly demonstrated that the use of thermotolerant inulin-utilizing yeast K. marxianus for ethanol production from fresh JA tubers in the CBP process not only provided high levels of ethanol, but also could eliminate the addition of external enzyme for inulin hydrolysis, which might lead to the reduction of operating costs. The expression of genes involved in carbohydrate metabolism in K. marxianus DBKKU Y-102 during ethanol fermentation was investigated by real-time RT-PCR, and the results revealed that expression levels were distinctive depending on the growth phase and growth conditions. However, among the genes tested, adh4 and tdh2 were highly expressed under high temperature conditions in both exponential- and stationary-growth phases, suggesting that these genes might play a crucial role in acquiring thermotolerance ability in this organism under stress conditions.