Residual agricultural biomass represents an untapped resource for renewable fuel production. Ethanol production from lignocellulosic biomass is not economically feasible, in part, due to limitations in biocatalyst performance. Obtaining a high ethanol yield from lignocellulosic biomass requires the use of a biocatalyst that rapidly produces ethanol with few byproducts, metabolizes all sugars produced by biomass treatment and resists toxins present in the feedstock and the fermentor.

Several ethanol resistant derivatives of the ethanologenic strain Escherichia coli FBR5 have been isolated. During pilot fermentor studies in a Luria broth medium containing 150 g/L xylose, strains ARL and ANE produced over 50 g/L of ethanol while FBR5 produces roughly 40 g/L of ethanol. Further fermentations were done with the goal of maximizing ethanol concentration. However, high concentrations of xylose (>175 g/L) were found to inhibit cell growth and ethanol production. Under fed-batch conditions where xylose concentrations were regulated at 100 g/L, ARL produced over 60 g/L ethanol. The fed-batch strategy combines the high ethanol yields and rapid ethanol production observed in batch fermentations with a product stream at a high ethanol concentration.