Bioethanol production by heterologous expression of two individual 1-FEH genes from Helianthus tuberosus in Saccharomyces cerevisiae 6525

Abstract

Bioethanol is a promising renewable source of energy. The heterologous expression of inulinases from microorganisms in the yeast Saccharomyces cerevisiae improves ethanol production from inulin. Fructan exohydrolases (FEHs) from fructan-rich plants hydrolyze fructofuranosyl units in inulin to produce fructose. Here, we examined whether the heterologous expression of FEHs could also improve ethanol production in yeast. First, we expressed two Jerusalem artichoke (Helianthus tuberosus) FEH genes (Ht1-FEH I and II) in Pichia pastoris yeast X-33 to examine the biochemical properties of the encoded enzymes. Ht1-FEH I was relatively stable at pH 4–8 and 4–35 °C and Ht1-FEH II was relatively stable at pH 4–8 and 4–40 °C. The K m and V m values of Ht1-FEH I were 0.68 and 0.00129 mg/min, while those of Ht1-FEH II were 0.92 and 0.0048 mg/min, respectively. The enzyme activities were affected by metal ions and protein inhibitors. Additionally, the transgenic expression of Ht1-FEH I and Ht1-FEH II in S. cerevisiae 6525 at pH 6, 30 °C resulted in 25 and 27 % increases in ethanol production compared to the non-FEH-transformed control (CK), respectively. The efficiency of ethanol production was greater in yeast expressing plant FEHs than in yeast expressing inulinases derived from some microorganisms. Thus, plant FEHs have potential applications in bioethanol production.