Recently, we reported on the construction of a whole-cell biotransformation system in Escherichia coli for the production Of D-mannitol from D-fructose (Kaup B, Bringer-Meyer S, Sahm H (2004) Metabolic engineering of Escherichia coli: construction of an efficient biocatalyst for D-mannitol formation in a whole-cell biotransformation. Appl Microbiol Biotechnol 64:333-339). Supplementation of this strain with extracellular glucose isomerase resulted in the formation Of 800 MM D-mannitol from 1,000 mM D-glucose. Co-expression of the xylA gene of E. coli in the biotransformation strain resulted in a D-mannitol concentration of 420 mM from 1,000 MM D-glucose. This is the first example of conversion Of D-glucose to D-mannitol with direct coupling of a glucose isomerase to the biotransformation system.