Contrary to E. coli, Z. mobilis is an ethanologenic bacterium and lacks the ability to metabolize hemi-celluloses derived monosaccharides, except glucose. There­fore, most of the engineering strategies applied to this bacterium intended to increase their substrate utilization range. In an earlier study, the strain CP4 has been shown to be the best ethanol producer from glucose. It was first engineered toward xylose utilization by the expression, on a plasmid, of the E. coli genes encoding for xylose isomerase (XI), xylulokinase (XK), transaldolase (TAL), and transketolase (TKL) under the control of strong constitutive promoters [206]. Ethanol yield from xylose fermentation attained 86% of the theoretical. The same approach was used to engineer the strain ATCC 39676 toward arabinose fer­mentation [35]. The genes from the E. coli operon araBAD, encoding L-arabinose isomerase (AI), L-ribulokinase (RK), L-ribulose-5P 4-epimerase (L-RPE), toge­ther with TAL and TKL allowed L-arabinose fermentation at high yield (96%) but at a low rate. This was ascribed to very low affinity of the glucose facilitator to L — arabinose. The same ATCC 39676 strain was used to express the xylose pathway, followed by successful long-term (149 d) adaptation in continuous fermentation of hemicellulose hydrolysates containing xylose, glucose, and acetic acid [106]. Finally, co-fermentation of glucose, xylose, and arabinose was obtained by genomic DNA integration (AX101 strain) of the xylose and arabinose pathways

[124] . The co-fermentation process yield was about 84%, with preferential order in sugar utilization: glucose first, then xylose, and arabinose last.