Historically, Saccharomyces has served as the main biocatalyst for commer­cial ethanol production. Considering that Saccharomyces and Z. mobilis are naturally ethanologenic, these organisms are obvious candidates for ethanol production. However, both organisms lack the native ability to utilize pentose sugars, the major component of the hemicellulose fraction of biomass [9,10]. Though E. coli lacks the native ability to produce ethanol as the major fer­mentation product, it utilizes both hexose and pentose sugars [11] and the uronic acid constituents of pectin [12]. The breadth of carbohydrates metab­olized, extensive background of knowledge, and ease of genetic manipulation made E. coli an obvious choice for metabolic engineering of a microbial bio­catalyst for production of ethanol from lignocellulose.

2.1