Submitted to: Society of Industrial Microbiology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: August 6, 1999
Publication Date: N/A
Technical Abstract: Biomass from agricultural residues is a potential low-cost feedstock for commercial ethanol production. Recombinant Escherichia coli that express the pet (production of ethanol) genes convert the glucose, xylose, and arabinose derived from lignocellulose to ethanol. To improve the stability of ethanol fermentations, we developed a series of ethanol-producing E. coli strains by transforming the pet operon into strains that cannot grow anaerobically. Due to mutations in the lactate dehydrogenase and pyruvate formate lyase genes, the cells are unable to reduce pyruvate and reoxidize the NADH generated in glycolysis. In our E. coli FBR strains, the pet genes (pyruvate decarboxylase and alcohol dehydrogenase encoded on pLOI297) complement the mutations and allow anaerobic growth by providing an alternate pathway for oxidation of NADH. In this scheme, the pet plasmid is exceptionally stable, without the addition of antibiotics. We have applied this strategy to E. coli strains having a variety of genetic backgrounds, including E. coli B. In serial batch cultures, an average of 96% of the cells maintained the pet plasmid after ten transfers. We are presently evaluating the performance of the new recombinants in fermentations of mixed sugars and corn fiber hydrolysates.