Monday, May 2, 2011
Grand Ballroom C-D, 2nd fl (Sheraton Seattle)
Pectin-rich materials are an abundant, underused resource. Waste material from industrial processes, such as the sugar beet pulp (SBP) remaining after sugar extraction, are often discarded or used as animal feed. Pectin-rich materials contain sugars that can be fermented into ethanol and used as renewable biofuel. However, large quantities of commercial enzymes are required to degrade the cell wall, releasing monomeric sugars for microbial fermentation. Escherichia coli KO11 was genetically engineered into multiple strains which produce heterologous saccharification enzymes thus decreasing the supplementation of pectin-rich fermentations with commercial enzymes. E. coli LY40A contains cellobiose phosphotransferase genes (casAB) from Klebsiella oxytoca, which allows uptake and utilization of cellobiose. Further engineering of LY40A 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 the secretion of PelE and Ogl. Fermentations were conducted using a mixture of pure sugars representative of the composition of SBP. The newly engineered strains were able to ferment cellobiose due to the casAB gene products resulting in increased ethanol production in comparison to KO11. Biomass fermentations of 10% (w/v) SBP were conducted using all strains. 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. Fermentation of the additional monomeric sugars released via Ogl activity produced more ethanol in these strains.