Bioenergy II: Comparison of Laboratory and Industrial Saccharomyces cerevisiae Strains for their Stress Tolerance

There are various kinds of stresses during the process of ethanol fermentation and more inhibitory factors are produced when lignocelluloses hydrolysate is used as the substrate. The pretreatment of lignocelluloses biomass causes the increase in the amount of acids and thus the decrease in pH. Low-molecular weight aliphatic acids, furaldehydes and a broad range of aromatic compounds are produced during the pretreatment process. They are the inhibitors for the ethanol producers, e.g. Saccharomyces cerevisiae. Furthermore, besides glucose, lignocellulose hydrolysate contains other sugars, such as xylose, arabinose, galactose and mannose etc., among which xylose is taking the major proportion. Stress tolerance and xylose utilization are therefore essential for Saccharomyces cerevisiae strains to get high-efficiency fermentation and high-yield ethanol production from lignocellulosic materials. In this study, a few laboratory and industrial Saccharomyces cerevisiae strains were selected for the evaluation of their potentials in pH tolerance, inhibitor resistance, temperature and ethanol tolerance, and xylose resistance. The results revealed that strains ATCC 96581 and ATCC 24860 are the most stress tolerant S. cerevisiae strains for ethanol fermentation. Such strains will be improved for inhibitor resistance and xylose utilization in the future by metabolic engineering and directed evolution.