Effect of inorganic salt stress on the thermotolerance and ethanol production at high temperature of Pichia kudriavzevii

Abstract

Application of cross-protection is expected to improve the thermotolerance of yeasts to enhance their ethanol production at high temperature. In this study, the effects of eight kinds of inorganic salts on the thermotolerance and ethanol production at high temperature in Pichia kudriavzevii were investigated. P. kudriavzevii showed strong thermotolerance and the ability to produce ethanol at high temperature, and higher ethanol production of P. kudriavzevii was observed at high temperature (37–42 °C) compared with that at 30 °C. Inorganic salt stresses induced obvious cross-protection of thermotolerance in P. kudriavzevii. The presence of 0.1 mol/L KNO3 or Na2SO4 or 0.2 mol/L NaCl, KCl, NaNO3, K2SO4 or MgCl2 increased the yeast biomass in YEPD medium at 44 °C to 2.72–3.46 g/L, obviously higher than that in the absence of salt stress (2.17 g/L). The addition of NaCl, KCl, NaNO3, KNO3, Na2SO4, K2SO4, CaCl2 and MgCl2 significantly increased the ethanol production of P. kudriavzevii in YEPD fermentation medium at 44 °C by 37–58%. KCl and MgCl2 exhibited the best performance on improving the thermotolerance and ethanol production, respectively, of P. kudriavzevii. A highly significant correlation (P < 0.01) was obtained among ethanol production, biomass and glucose consumption, suggesting the important role of thermotolerance and glucose consumption in enhanced ethanol production. The combination of NaCl, KCl and MgCl2 had a synergistic effect on the improvement of thermotolerance and ethanol production at high temperature in P. kudriavzevii. This study provides some important clues for improving ethanol production of thermotolerant yeasts at high temperature.