Monday, July 25, 2011: 8:30 AM
Oak Alley, 4th fl (Sheraton New Orleans)
Due to its excellent capability to ferment C5 sugars, Escherichia coli has been considered one of the platform organisms to be engineered for production of cellulosic ethanol. In this study, we engineered a non-transgenic E. coli strain by establishing a native homoethanol pathway (glucose (or 1.2 xylose) => 2 pyruvate + 2 NADH => 2 acetyl-CoA + 4 NADH => 2 ethanol) through deletions of genes encoding competing fermentation pathways and anaerobic expression of pyruvate dehydrogenase. The resulting non-transgenic strain, SZ420, fermented xylose to ethanol at greater than 90% theoretic yield. Subsequently, we selected a fast growing ethanol tolerant mutant of SZ420 through a three-month metabolic evolution for improved cell growth, followed by a two-month adaptive evolution for enhanced ethanol tolerance. The evolved mutant, SZ470, was able to grow anaerobically in LB medium containing 40 g L-1of ethanol. We further improved SZ470 by improving expression of native alcohol dehydrogenase (adhE). The resulting non-transgenic strain, RM10, was able to complete 120 g L-1 of xylose (and/or arabinose) fermentation with an ethanol titer of 56 g L-1.