The potential of the newly isolated thermotolerant yeast Pichia kudriauzeuii RZ8-1 for high-temperature ethanol production

High potential, thermotolerant, ethanol-producing yeasts were successfully isolated in this study. Based on molecular identification and phylogenetic analysis, the isolated thermotolerant yeasts were clustered in the genera of Pichia kudriaozeoii, Candida tropicalis, Candida orthopsilosis, Candida glabrata and Kodamea ohmeri. A comparative study of ethanol production using 160 g/L glucose as a substrate revealed several yeast strains that could produce high ethanol concentrations at high temperatures. When sugarcane bagasse (SCB) hydrolysate containing 85 g/L glucose was used as a substrate, the yeast strain designated P. kudriaozeoii RZ8-1 exhibited the highest ethanol concentrations of 35.51 g/L and 33.84 g/L at 37 degrees C and 40 degrees C, respectively. It also exhibited multi-stress tolerance, such as heat, ethanol and acetic acid tolerance. During ethanol fermentation at high temperature (42 degrees C), genes encoding heat shock proteins (ssg1 and hsp90), alcohol dehydrogenases (adh1, adh2, adh3 and adh4) and glyceraldehyde-3-phosphate dehydrogenase (tdh2) were up-regulated, suggesting that these genes might play a crucial role in the thermotolerance ability of P. kudriaozeoii RZ8-1 under heat stress. These findings suggest that the growth and ethanol fermentation activities of this organism under heat stress were restricted to the expression of genes involved not only in heat shock response but also in the ethanol production pathway. (C) 2017 Sociedade Brasileira de Microbiologia. Published by Elsevier Editora Ltda.