Fermentation performance of ethanologens in lignocellulosic hydrolysates produced from corn stover and switchgrass

To identify and overcome key barriers to the sustainable conversion of lignocellulosic biomass to biofuels, we produced lignocellulosic hydrolysates with corn stover (CS) and switchgrass (SG) feedstocks, which were pretreated with ammonia fiber expansion (AFEX^TM) or alkaline hydrogen peroxide (AHP), and also produced high concentrated hydrolysate (9% glucan loading) with corn stover.  Chemical compositions of these lignocellulosic hydrolysates were analyzed, including heavy metals and minerals, amino acids, potential lignin-derived inhibitors (phenolic lignotoxins), acetate/acetamide, and other inhibitors. We then carried out fermentation experiments with these hydrolysates using three ethanologens: Saccharomyces cerevisiae, Zymomonas mobilis, and Escherichia coli.  During the fermentation, the end products were collected and analyzed by HPLC, and RNA samples were also collected for RNAseq analysis to generate high sensitivity profiles for microbial responses in these different hydrolysates.  Z. mobilis showed very similar growth and glucose/xylose utilization in AFEX-CS hydrolysate (ACSH) and AFEX-SG hydrolysate (ASGH), while S. cerevisiae grew significant better in ACSH than other hydrolysates.  Both Z. mobilis and S. cerevisiae showed slow growth and sugar utilization in 9% glucan-loading ACSH, and E. coli failed to grow in this hydrolysate.  We found that overall most ethanologens grew better in hydrolysates that were pretreated with AFEX than that was pretreated with AHP. The detailed chemical analysis of these hydrolysates, and fermentation performance and the gene expression profile of ethanologens will be presented.