Feedstock pretreatments such as Ammonia-Fiber-Expansion (AFEX) and acid pretreatment dictate the fermentability of the resulting hydrolysate. There is a common perception that hydrolysate from lignocellulosic materials is inherently nutrient-deficient. However, hydrolysate generated from AFEX pretreatment exhibits high fermentability without any conditioning and nutrient supplementation.   

Additionally, metabolic engineering for effective ethanol production has been extensively pursued in recent decades. Reports on different ethanologens indicate highly promising results. However, comparison across the strains is difficult due to different experimental settings. The performance of these strains on unconditioned hydrolysate cannot be determined because many experiments have involved extensive detoxification and/or nutrient supplementation prior to fermentation.

We have studied the fermentation performance of several recombinant ethanologens side-by-side using AFEX, acid-pretreated and steam-pretreated corn stover. These ethanologens  include Escherichia coli KO11 (U. of Florida), Saccharomyces cerevisiae 424A(LNH-ST) (Purdue University) and Zymomonas mobilis AX101 (National Renewable Energy Lab).

From these investigations, we have obtained comparative data for ethanol yield, productivity and growth robustness in cellulosic hydrolysates. As a result, the most promising ethanologen(s) suited for ethanol production from various pretreatment methods were identified. Based on these strains, we have optimized fermentation conditions with industrially-relevant parameters in both Separate-Hydrolysis-and-Fermentation (SHF) and Simultaneous-Saccharification-and-Co-Fermentation (SSCF) using AFEX-pretreated corn stover as the main feedstock.