Monday, August 13, 2012
Columbia Hall, Terrace Level (Washington Hilton)
The National Renewable Energy Laboratory has devoted great efforts to the development of an ethanologen, Zymomonas mobilis for efficient conversion of lignocellulosic feedstocks to ethanol. Through metabolic engineering, mutagenesis, and adaptation, we have constructed several recombinant strains that can use the three major sugars (glucose, xylose, and arabinose) in the pretreated/saccharified corn stover. Following glucose and xylose, arabinose is the third most abundant sugar in corn stover and accounts for approximately 5% of the total potentially available sugars in corn stover feedstock. Furthermore, arabinose makes up approximately 11% of the pentose sugars released from hemicellulose in the dilute acid pretreatment process. Achieving an 85% arabinose-to-ethanol yield decreases the minimum ethanol selling price by about $0.08-$0.10/gal. However, a major limitation of these strains is that the rate of arabinose utilization is relatively slow (a problem exacerbated by the inhibitors present in hydrolysate), and the achievement of high levels of arabinose conversion has proven challenging. In order to increase the efficiency of arabinose conversion, we have incorporated several strategies, including random genomic-integration mutagenesis and adaptation to further improve the arabinose-utilizing strains. In this work as a result of the strategies applied, we demonstrate superior growth rate and arabinose utilization of the newly generated glucose/xylose/arabinose strains. Superior strains are currently being characterized to understand the relationship between the genetic changes and the phenotypic effects.