Single-step bioconversion for the preparation of L-gulose and L-galactose

Both carbohydrate monomers L-gulose and L-galactose are rarely found in nature, but are of great importance in pharmacy R&D and manufacturing. A method for the production of L-gulose and L-galactose is described that utilizes recombinant Escherichia coli harboring a unique mannitol dehydrogenase. The recombinant E. coli system was optimized by genetic manipulation and directed evolution of the recombinant protein to improve conversion. The resulting production process requires a single step, represents the first readily scalable system for the production of these sugars, is environmentally friendly, and utilizes inexpensive reagents, while producing L-galactose at 4.6 g L(-1)d(-1) and L-gulose at 0.90 g L(-1)d(-1).