Submitted to: American Chemical Society Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: April 17, 1997
Publication Date: N/A
Technical Abstract: Ethanologenic Escherichia coli strains have shown excellent yields for conversion of biomass sugars to ethanol. The PET operon containing the alcohol dehydrogenase and pyruvate decarboxylase genes from Zymomonas mobilis has been introduced into these strains causing sugar fermentation to be redirected almost exclusively to ethanol production. However, when cultured continuously, ethanol yield and productivity have been reported t decline with time. We have been able to stabilize ethanol production by introducing the PET operon into E. coli strain K12/FMJ39, which is unable to grow anaerobically because its fermentative pathways have been genetically disrupted. The resulting strain grows anaerobically and is genetically stable, without the addition of antibiotic, provided anaerobiosis is maintained. When cultured in a chemostat for 48 generations (23 with and 25 without antibiotic), cells retained the plasmid dand continued to produce ethanol at a constant rate. When grown in batch culture on either arabinose, glucose, or xylose, ethanol yields were 0.40-0.42 (g ethanol per g sugar consumed) and fermentations were completed within 48 h. A similar strategy is currently being pursued for L-lactate production, where K12/FMJ39 has been transformed with a plasmid containing a lactate dehydrogenase gene from Streptococcus bovis. The resulting "homolactic" strain produced 6% w/v lactate in batch culture on glucose and is expected to be useful for producing L-lactate from lignocellulosic hydrolysates.