Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: 5/25/2000
Publication Date: N/A
Technical Abstract: Agricultural biomass has the potential to supplement cornstarch as a feedstock for commercial ethanol production. Hydrolysis of lignocellulosic biomass yields a mixture of hexose and pentose sugars, which can be converted to ethanol by recombinant E. coli strains that express pyruvate decarboxylase and alcohol dehydrogenase. To improve the ability of E. coli to efficiently ferment mixed sugars, we tested a catabolite repression (ptsG) mutant for the ability to metabolize mixtures of glucose, xylose, and arabinose. In aerobic culture, the wild-type strain metabolized glucose before xylose and arabinose, while the ptsG mutant metabolized the sugars simultaneously. The wild-type and ptsG strains were transformed with the pet (production of ethanol) genes and used to ferment mixed sugars to ethanol. The ptsG mutant produced 3.3% (w/v) ethanol from a 4% glucose/4% xylose mixture, compared to the wild-type strain, which produced 2.9% ethanol and left 1.4% xylose unconsumed. The ptsG mutation was introduced into ethanol-producing E. coli strains with different genetic backgrounds. The ptsG mutant FBR14 consumed glucose and xylose simultaneously, compared to its parent, FBR5, which used xylose only after glucose was depleted. Both fermentations took the same amount of time to complete (44 hr), because FBR14 ferments glucose more slowly than FBR5. However, a mixture of FBR5 and FBR14 completed the fermentation in 33 hr. A coculture of ptsG- and ptsG+ strains may provide the most efficient fermentation of a lignocellulosic substrate such as corn fiber.