Conversion of corn fiber to ethanol by recombinant E-coli strain FBR3

We have developed a novel ethanologenic Escherichia coli strain FBR3 that i s an efficient biocatalyst for converting mixed sugar streams (eg, arabinos e, glucose, and xylose) into ethanol, In this report, the strain was tested for conversion of corn fiber hydrolysates into ethanol. Corn fiber hydroly sates with total sugar concentrations of 7.5% (w/v) were prepared by reacti ng corn fiber with dilute sulfuric acid at 145 degrees C, Initial fermentat ions of the hydrolysate by strain FBR3 had lag times of approximately 30 h judged by ethanol production, Further experiments indicated that the acetat e 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 wer e 90% of theoretical, Maximum ethanol concentrations were 2.80% w/v, and th e fermentations were completed in approximately 50 h. The optimal pH for th e fermentation was 6.5, Below this pH, sugar consumption was incomplete and above it, excess base addition was required throughout the fermentation. T wo alternative neutralization methods (overliming and overliming with sulfi te addition) have been reported for improving the fermentability of lignoce llulosic hydrolysates. These methods further reduced the lag phase of the f ermentation, albeit by a minor amount.