High temperature alcoholic fermentation by new thermotolerant yeast strains Pichia kudriavzevii isolated from sugarcane field soil

Abstract

The thermotolerant and ethanogenic yeasts are an important factor in numerous ethanol industrial applications. In this study, the potential of new isolates of thermotolerant, ethanol-producing yeasts was successfully demonstrated. In total, 60 yeast isolates were obtained from soil sugarcane fields in Uttaradit, Kamphang Phet, Chai Nat, Sukhothai, Nakhon Sawan and Phitsanulok provinces, Thailand and subjected to characterization of thermotolerance using an enrichment technique with 4% (volume per volume) ethanol. The growth performance and fermentation activity under stress conditions were compared with that of Thai industrial Saccharomyces cerevisiae TISTR 5606. Interestingly, the results showed that 30 isolates grew at high temperatures (up to 45 °C). Three isolates (NUNS-4, NUNS-5 and NUNS-6) could tolerate those conditions on agar composed of yeast extract, peptone and glucose containing 13% (v/v) ethanol. Furthermore, gas chromatography analysis to determine the ethanol concentration revealed the three new isolates produced higher amounts of ethanol than S. cerevisiae TISTR 5606 at fermentation temperatures of 40 °C and 45 °C (p < 0.05) when utilizing glucose as the carbon source. The isolate NUNS-4 had the highest ethanol concentrations of 88.60 ± 0.75 g/L and 54.30 ± 0.97 g/L at 40 °C and 45 °C, respectively. Furthermore, phylogenetic analysis based on the D1/D2 domain of 26S rDNA showed that the new isolates were identified as Pichia kudriavzevii. Consequently, thermo-tolerant and ethanol-tolerant P. kudriavzevii NUNS-4, NUNS-5 and NUNS-6 are possible candidates as strains for commercial-scale ethanol production when using glucose as the fermentation substrate.