Exogenous L-proline Increases Stress Tolerance of Yeast Pichia kudriavzevii Against Inhibitors in Lignocellulose Hydrolysates and Enhances its Ethanol Production

Abstract

Three ethanologenic yeast isolates (E, R and T) capable to use both pentose and hexose sugars as substrate for ethanol fermentation was isolated. Thus, suggesting its potential for 2nd generation of ethanol production by using lignocellulose hydrolysate. Based on ITS sequence, those three isolates were identified as yeast Pichia kudriavzevii. Prior its utilization as fermentation substrate, lignocellulose is subjected to complex hidrolysis reactions, which results certain toxic compounds (furfural and organic acid). Our results indicate that P. kudriavzevii isolates were sensitive toward 0.15% furfural and 0.375% acetic acid. Interestingly, supplementation of 1.5% L-proline in the medium significantly enhanced the survival rate of all P. kudriavzevii isolates against the particular toxic compounds. Moreover, supplementation of L-proline also enhanced the production of ethanol in glucose as substrate, in a dose dependent manner. Indeed, addition of 1.5% L-proline could increase the ethanol yield of isolate E, R and T for approximately 57%, 53%, and 62%, respectively, as compared to that 0.5% L-proline. The highest ethanol production was exhibited by isolate T (14g/100mL) in 1.5% L-proline treatment. Our data indicate, that L-proline supplementation may potentially be applied to enhance ethanol production by P. kudriavzevii isolates, particularly for its future application in lignocellulose-based ethanol productions.