Tuesday, May 3, 2011
Lignocellulosic biomass is a promising renewable feedstock for the microbial production of fuels. To release the major fermentable sugars such as glucose and xylose, pretreatment, hydrolysis, and subsequent conditioning of biomass feedstocks are needed. During this process, many toxic compounds are produced or introduced which subsequently inhibit microbial growth and in many cases, production of ethanol. An understanding of the toxic effects of compounds found in hydrolysate on the fermentation microorganism is critical to improving ethanol yields in the process. One of the inhibitory compounds is acetic acid, liberated from hemicelluloses, which strongly inhibits the cell growth and ethanol production especially from xylose. To further explore the effect of acetate on a cellular level, we designed a microarray based the most up-to-date genome annotation for both coding sequences and intergenic regions, and conducted genome-wide analysis of gene expression levels to determine the effects of acetate. RNA samples were extracted from Z. mobilis 8b cells taken from log phase cultures in glucose or xylose with either 0 or 3.5 (for xylose) or 10 (for glucose) g/L acetic acid (as ammonium salt) at a controlled pH of 6.0. We report the results of this transcriptomic analysis, focusing on genes that are identified as differentially expressed when cells are grown on glucose vs xylose as well as inhibited by acetic acid on either sugars.