Abstract
DNA microarray analysis was used to investigate the expression profile ofSaccharomyces cerevisiae genes in glycolysis pathway, trehalose and steroid biosynthesis and heat shock proteins (HSP) in response to harsh environment under the late stage of very high gravity (VHG) fermentation. The data show that only a few genes (GPM2, PGM1, GAL10 and PGM1) involved in glycolysis pathway and trehalose biosynthesis were up-regulated. Five genes that encode heat shock proteins (HSP26, HSP10, HSP42, HSP78 and HSP82) were up-regulated. Among these five genes, there was a strong expression increase of about 84-fold for HSP26.The results of this study revealed adverse VHG fermentation conditions stress response pattern and suggested interesting information about the mechanisms involved in adaptation of cells to the complex VHG fermentation environment. This identification of genes provides information that will help to genetically modify yeast to further maintain the fermentation fitness and improve its fermentation capacity and process. Key words: DNA microarray, gene expression, yeast, stress, very high gravity (VHG) fermentation.
Highlights
Fuel ethanol, the most common renewable liquid fuel from biomass resources conversion, is a global energy commodity that is competitive with fossil fuels
In order to avoid the damage of high sugar osmotic stress exerted on S. cerevisiae cells at the beginning of very high gravity (VHG) fermentation, fed-batch experiment was adopted in VHG fermentation process as described earlier
It showed a significant productivity decline to the fermentation end. This phenomenon could be caused by the growth, and fermentation progression was hampered by a decline in yeast viability and fermentation capacity of S. cerevisiae which appeared to be a consequence of osmotic pressure, ethanol stress and other metabolic inhibitors accumulation in broth
Summary
The most common renewable liquid fuel from biomass resources conversion, is a global energy commodity that is competitive with fossil fuels. Most conventional ethanol fermentation processes are carried out with low carbohydrate concentration (usually less than 200 g L-1 of glucose) to prevent either glucose or ethanol stresses on yeast cells (Pham and Wright, 2007). Compared with conventional ethanol fermentation processes, the VHG fermentation has several distinct advantages such as the increase of ethanol concentration and process productivity, reduced capital costs, energy costs and the risk of bacterial contamination (Laopaiboon et al, 2009). VHG fermentation has been gradually applied by the ethanol industry to reduce costs (Theerarattananoon et al, 2008). It is frequently accompanied with stuck or sluggish characteristics near the end of fermentation process.
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