FUEL ETHANOL FROM HARDWOOD HEMICELLULOSE HYDROLYSATE BY GENETICALLY ENGINEERED ESCHERICHIA-COLI-B CARRYING GENES FROM ZYMOMONAS-MOBILIS

Escherichia coli B (ATCC 11303) carrying the 'PET' operon on plasmid pLOI 297 converted hemicellulose hydrolysate to ethanol at an efficiency of 94% theoretical maximum, which is 15% better than the highest efficiency reported for pentose utilizing yeasts in a comparable system. Aspen prehydrolysate (APH), that had been produced by the Bio-Hol Process using a Wenger extruder with SO2 as catalyst, was used as feedstock. The fermentation medium contained predominantly xylose (35g/L) with acetic acid present at about 6 g/L. With the pH controlled at 7.0, this concentration of acetic acid was not inhibitory for growth or xylose fermentation. When the APH was fortified with nutrients (tryptone and yeast extract), the recombinant (inoculated at 0.5 g dry wt/L) converted 100% of the xylose to ethanol with a volumetric productivity of 0.29 g/L/hr. Overliming the APH with Ca(OH)2, followed by neutralization to pH 7 with sulphuric acid and removal of the insolubles, resulted in a 2-fold increase in productivity. The max. productivity was 0.76 g/L/hr. The productivity in Ca(OH)2-treated APH, fortified with only mineral salts, was 0.26 g/L/hr.