David S Beall

Conversion of hydrolysates of corn cobs and hulls into ethanol by recombinant Escherichia coli B containing integrated genes for ethanol production.

SummaryHemicellulose and residual starch in corn hulls from wet milling and hemicellulose in corn cobs were hydrolyzed by incubation in dilute sulfuric acid at 140°C to 160°C. These hydrolysates were efficiently fermented to ethanol by a genetically engineered derivative ofE. coli B, strain KO11. Fermentation of com hull hydrolysate was complete after 48 h with a final ethanol concentration of 38 grams per liter. Fermentation of corn cob hydrolysate was essentially complete after 24 h due to a lower concentration of sugars and higher levels of inocula. In both cases, ethanol produced was equivalent to 100% of the maximum theoretical yield (0.51 grams ethanol/gram sugar) based on momoner sugar content. ThusE. coli B strain KO11 appears to be an excellent candidate for the efficient production of ethanol from hydrolysates of corn residues.

Production of recombinant bacterial endoglucanase as a co-product with ethanol during fermentation using derivatives of Escherichia coli KO11

This study demonstrates a new approach to reduce the amount of fungal cellulase required for the conversion of cellulose into ethanol. Escherichia coli KO11, a biocatalyst developed for the fermentation of hemicellulose syrups, was used to produce recombinant endoglucanase as a co-product with ethanol. Seven different bacterial genes were expressed from plasmids in KO11. All produced cell-associated endoglucanase activity. KO11(pLOI1620) containing Erwinia chrysanthemi celZ (EGZ) produced the highest activity, 3,200 IU endoglucanase/L fermentation broth (assayed at pH 5.2 and 35 degrees C). Recombinant EGZ was solubilized from harvested cells by treatment with dilute sodium dodecyl sulfate (12.5 mg/ml, 10 min, 50 degrees C) and tested in fermentation experiments with commercial fungal cellulase (5 filter paper units/g cellulose) and purified cellulose (100 g/L). Using Klebsiella oxytoca P2 as the biocatalyst, fermentations supplemented with EGZ as a detergent-lysate of KO11(pLOI1620) produced 14%-24% more ethanol than control fermentations supplemented with a detergent-lysate of KO11(pUC18). These results demonstrate that recombinant bacterial endoglucanase can function with fungal cellulase to increase ethanol yield during the simultaneous saccharification and fermentation of cellulose.