Submitted to: Biotechnology for Fuels and Chemicals Symposium Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 5/9/2001
Publication Date: N/A
Technical Abstract: Development of suitable biocatalysts for the biomass to fuels and chemicals industry remains a significant technical challenge. We have developed a series of stable Escherichia coli strains that convert biomass sugars (xylose and glucose) to either L-lactate or ethanol by transforming nonfermentative strains with plasmids carrying either the lactate dehydrogenase (ldh) gene from Streptococcus bovis or alcohol dehydrogenase and pyruvate decarboxylase genes from Zymomonas mobilis. Under anaerobic conditions, these plasmids were retained in the absence of antibiotics by over 95% of the cells. Modified strains produced L-lactate or ethanol from glucose at 90-93% of theoretical. Recombinant strains were also evaluated for the ability to ferment xylose and mixtures of xylose and glucose. Strains efficiently fermented xylose alone; however, because glucose was used in preference of xylose, cultures containing mixtures of these sugars inefficiently fermented the xylose provided. To overcome this, a catabolite repression mutant (ptsG) was constructed that simultaneously used glucose and xylose and produced ethanol at 94% of theoretical. This research demonstrated that metabolic engineering approaches can be used to modify E. coli to provide for more efficient fermentation of hemicellulose containing biomass hydrolysates.