Tuesday, May 3, 2011
Arabinose is the third most abundant sugar in corn stover following glucose and xylose, accounting for about 5% of the total potentially available sugar in corn stover feedstock. Arabinose makes up approximately 11% of pentose sugars released from hemicellulose in dilute acid pretreatment process. Achieving an 85% arabinose-to-ethanol yield decreases the MESP by about $0.08-$0.10/gal. In order to fully utilize the sugars in the biomass feedstocks for ethanol production, we genetically engineered the ability to ferment arabinose to ethanol into the Z. mobilis 8b, a previously constructed strain capable of fermenting of both glucose and xylose. This was achieved by introducing araA (encoding arabinose isomerase), araB (encoding L-ribulokinase) and araD (encoding L-ribulose-5-phosphate-4-epimerase) from E. coli under the expression of constitutive native gap promoter on plasmids or via genomic integration. Initially the recombinant strains grew poorly in the medium containing arabinose as the sole carbon source. After several serial transfers in arabinose medium, culture growth improved significantly. The fermentation performance of selected isolates was evaluated in pure sugar medium as well as in the pretreated corn stover hydrolysates.