The current global environmental tr

The current global environmental trend to ward"carbon neutral"technologies for sustainable biofuel production has received considerable attention. As a result, much effort has been' made to improve the process of bioethanol production because it is one of the most attractive alternatives to gasolin (1, 2). Saccharomyces cerevisíae is the dominant microorganism used to produce ethanol. Numerous studies on genetic analysis and modifi cations to the fermentation ability or stress tolerance of S. cerevísiae have been reported (2-5). These studies have yielded a number of yeast strains exhibiting improved fermentation ability or growth under stressful conditions. However, further improvement of stress tolerance is still needed in order to optimize the use of S. cerevísiaë in industrial applications. Acid-tolerance and thermo-tolerance are boch important traits for ethanol fermentation by S. cerevisíae. It is favorable to perform fermentation at a low pH in order to prevent bacterial contamination. Addition, for ethanol production from lignocellulosic biomass using acid hydrolyzate, fermentation under low PH conditions reduces neutralization costs. Fermentation at