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

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 degrees C) is not optimum (40-50 degrees C) for enzymatic hydrolysis in the simultaneous saccharification and fermentation (SSF) process. In this study, we successfully performed an SSF process at 42 degrees C from a high solid loading of 20% (w/v) acid-impregnated steam explosion (AISE)-treated rice straw with low inhibitor concentrations (furfural 0.19gl(-1) and acetic acid 0.95gl(-1)) using an isolate Pichia kudriavzevii SI, where the ethanol titre obtained (33.4g(p)l(-1)) was nearly 39% greater than that produced by conventional S.cerevisiae BCRC20270 at 30 degrees C (24.1g(p)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 1.07-1.21gl(-1), 5-hydroxymethyl furfural 0.20-0.72gl(-1) and acetic acid 4.80-7.65gl(-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.