CONVERSION OF CORN FIBER TO ETHANOL BY RECOMBINANT E. COLI STRAIN FBR3

Authors: Dien, Bruce; Iten, Loren; Bothast, Rodney

Submitted to: Journal of Industrial Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: In 1997, approximately one billion gallons of fuel ethanol were produced from corn starch. Demand for ethanol, as a substitute for petroleum, is expected to increase because of concerns related to national security, economic stability, environmental impact, and global warming. Expanding fuel ethanol production will require developing alternative feedstocks. In norder to expand fuel ethanol production, we are exploring the fermentation of sugars derived from corn fiber and agricultural wastes plus developing new ethanol-producing microorganisms to use these materials. We have recently developed a novel recombinant bacterial strain (FBR3) suitable for converting corn fiber hydrolysate to ethanol. The corn fiber was readily hydrolyzed with dilute sulfuric acid and the sugars recovered in a syrup. Strain FBR3 readily fermented these sugars and produced ethanol at 90% of the theoretical maximum.

Technical Abstract: We have developed a novel ethanologenic Escherichia coli strain FBR3 that is an efficient biocatalyst for converting mixed sugar streams (e.g., arabinose, glucose, and xylose) into ethanol. In this report, the strain was tested for conversion of corn fiber hydrolysates into ethanol. Corn fiber hydrolysates with total sugar concentrations of 7.5% (w/v) were prepared by reacting corn fiber with dilute sulfuric acid at 145 deg C. Initial fermentations of the hydrolysate by strain FBR3 had lag times of approximately 40 h. Further experiments indicated that the acetate present in the hydrolysate could not solely account for the long lag. The lag phase was greatly reduced by growing the pre-seed and seed cultures on corn fiber hydrolysate. Ethanol yields for the optimized fermentations were 90% of theoretical. Maximum ethanol concentrations were 2.80% w/v, and the fermentations were completed in approximately 50 h. The optimal pH for the efermentation was 6.5. Below this pH, sugar consumption was incomplete and above this addition was required throughout the fermentation. Two alternative methods (overliming and overliming with sulfite addition) have been reported for improving the fermentability of lignocellulosic hydrolysates. These methods further reduced the lag phase of the fermentation, albeit by a minor amount.