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

Abstract

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 kudriavzevii, Candida tropicalis, Candida orthopsilosis, Candida glabrata and Kodamea ohmeri. A comparative study of ethanol production using 160g/L glucose as a substrate revealed several yeast strains that could produce high ethanol concentrations at high temperatures. When sugarcane bagasse (SCB) hydrolysate containing 85g/L glucose was used as a substrate, the yeast strain designated P. kudriavzevii RZ8-1 exhibited the highest ethanol concentrations of 35.51g/L and 33.84g/L at 37°C and 40°C, respectively. It also exhibited multi-stress tolerance, such as heat, ethanol and acetic acid tolerance. During ethanol fermentation at high temperature (42°C), genes encoding heat shock proteins (ssq1 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. kudriavzevii 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.

Keywords: Ethanol production; Gene expression; Pichia kudriavzevii; Sugarcane bagasse hydrolysate; Thermotolerant yeast.

Fig. 1

Neighbor-joining showing phylogenetic tree position of the isolated thermotolerant yeasts based on the nucleotide sequence of the D1/D2 domain of the 26S rDNA gene.

Fig. 2

Effect of heat, ethanol and acetic acid stresses on the cell growth of P. kudriavzevii RZ8-1.

Fig. 3

Morphology of P. kudriavzevii RZ8-1 cells as determined by bright field microscopy at 40× magnification and SEM.