Monday, July 25, 2011
Grand Ballroom, 5th fl (Sheraton New Orleans)
Pectin-rich biomass such as sugar beet pulp, citrus waste, and apple pomace are viable feedstock sources for alternative fuels as they are not used for human consumption and animal feed use is of marginal economic value. In order for these feedstocks to be used, polymers must be hydrolyzed so that monomeric sugar molecules are released which the ethanologen can ferment. Ethanologenic Escherichia coli was engineered to contain cellobiose phosphotransferase genes (casAB) from Klebsiella oxytoca, which allows uptake and utilization of cellobiose. Further engineering produced strains containing pectate lyase (pelE) and oligogalacturonide lyase (ogl) from Erwinia chrysanthemi allowing E. coli to degrade pectin into short chain and monomeric sugars, respectively. Sec-dependent out pathway (out) genes were added for secretion of PelE and Ogl. Sugar beet pulp was chosen as the pectin-rich biomass for fermentations to produce fuel ethanol. Fermentations conducted with strains possessing casAB and pelE were able to produce small nonfermentable oligosaccharides of galacturonic acid. Addition of ogl to these strains enabled further degradation of pectin oligosaccharides into monomers and resulted in increased ethanol production in these strains. Although this recombinant bacterium expresses enzymes for pectin degradation, to increase ethanol titers, additional enzyme supplementation is needed. Partial saccharification and co-fermentation experiments combining the engineered ethanologenic bacterium with enzyme cocktails produced by Hypocrea jecorina grown on a variety of substrates resulted in varying levels of ethanol production. Recovery of ferulic acid from sugar beet pulp provides an additional co-product of high value, thus enhancing the overall economic viability of the process.