Repeated production of l-xylulose by an immobilized whole-cell biocatalyst harboring l-arabinitol dehydrogenase coupled with an NAD+ regeneration system

• We investigated l-xylulose production by E. coli harboring l-arabinitol dehydrogenase.
• We optimized conditions for l-xylulose production by recombinant E. coli whole cells.
• Coupling with NADH oxidase enhanced l-xylulose production by LAD up to 96% efficiency.
• Immobilized whole cells maintain 65% of the yield after 7 cycles of successive re-use.

The biotransformation of l-arabinitol into l-xylulose was investigated using whole-cell biocatalysts. Efficient production of l-xylulose was accomplished using Escherichia coli that expressed l-arabinitol dehydrogenase (LAD). The production yield was enhanced by coupling LAD with a cofactor-regenerating NADH oxidase in an E. coli whole-cell biocatalyst system. Factors affecting the production of l-xylulose by this whole-cell biocatalyst system include reaction pH, maximal cell loading, and cofactor regeneration. Under optimized conditions, the conversion of l-arabinitol into l-xylulose was achieved with above 96% efficiency, a rate much higher than that reported in previous studies. Furthermore, the whole-cell system could be immobilized on calcium alginate; the immobilized cells showed good operational stability, retaining their relative productivity at 65% after 7 cycles of successive re-use.