Fermentation of sugar cane bagasse hemicellulosic hydrolysate and sugar mixtures to ethanol by recombinant Escherichia coli KO11

CAROLINE MAKI TAKAHASHI; KATIA GIANNI DE CARVALHO LIMA; DEBORA FUMIE TAKAHASHI; FLAVIO ALTERTHUM

WORLD JOURNAL OF MICROBIOLOGY & BIOTECHNOLOGY

SPRINGER

Año: 2000 vol. 16 p. 829 - 834

0959-3993

Escherichia coliKO11, carrying the ethanol pathway genes pdc (pyruvate decarboxylase) and adh (alcohol dehydrogenase) from Zymomonas mobilisintegrated into its chromosome, has the ability to metabolize pentoses and hexoses to ethanol, both in synthetic medium and in hemicellulosic hydrolysates. In the fermentation of sugar mixtures simulating hemicellulose hydrolysate sugar composition (10.0 g of glucose/l and 40.0 g of xylose/l) and supplemented with tryptone and yeast extract, recombinant bacteria produced 24.58 g of ethanol/l, equivalent to 96.4% of the maximum theoretical yield. Corn steep powder (CSP), a byproduct of the corn starch-processing industry, was used to replace tryptone and yeast extract. At a concentration of 12.5 g/l, it was able to support the fermentation of glucose (80.0 g/l) to ethanol, with both ethanol yield and volumetric productivity comparable to those obtained with fermentation media containing tryptone and yeast extract. Hemicellulose hydrolysate of sugar cane bagasse supplemented with tryptone and yeast extract was also readily fermented to ethanol within 48 h, and ethanol yield achieved 91.5% of the theoretical maximum conversion effciency. However, fermentation of bagasse hydrolysate supplemented with 12.5 g of CSP/l took twice as long to complete.