Ethanol production from dilute-acid steam exploded lignocellulosic feedstocks using an isolated multistress-tolerant Pichia kudriavzevii strain

Abstract

Renewable and low-cost lignocellulosic wastes have attractive applications in bioethanol production. The yeast Saccharomyces cerevisiae is the most widely used ethanol-producing microbe; however, its fermentation temperature (30–35°C) is not optimum (40–50°C) for enzymatic hydrolysis in the simultaneous saccharification and fermentation (SSF) process. In this study, we successfully performed an SSF process at 42°C from a high solid loading of 20% (w/v) acid-impregnated steam explosion (AISE)-treated rice straw with low inhibitor concentrations (furfural 0.19 g l−1 and acetic acid 0.95 g l−1) using an isolate Pichia kudriavzevii SI, where the ethanol titre obtained (33.4 gp l−1) was nearly 39% greater than that produced by conventional S. cerevisiae BCRC20270 at 30°C (24.1 gp l−1). In addition, P. kudriavzevii SI exhibited a high conversion efficiency of > 91% from enzyme-saccharified hydrolysates of AISE-treated plywood chips and sugarcane bagasse, although high concentrations of furaldehydes, such as furfural 1.07–1.21 g l−1, 5-hydroxymethyl furfural 0.20−0.72 g l−1 and acetic acid 4.80–7.65 g l−1, were present. This is the first report of ethanol fermentation by P. kudriavzevii using various acid-treated lignocellulosic feedstocks without detoxification or added nutrients. The multistress-tolerant strain SI has greater potential than the conventional S. cerevisiae for use in the cellulosic ethanol industry.