Efficient L-xylulose production using whole-cell biocatalyst with NAD+ regeneration system through co-expression of xylitol dehydrogenase and NADH oxidase in Escherichia coli

L-Xylulose is a potentially valuable rare sugar used as starting material for antiviral and anticancer drug development in pharmaceutical industries. In this study, cofactor engineering was applied to improve the efficiency of L-xylulose production from xylitol. A water-forming NAD+ regeneration enzyme (NADH oxidase) from Streptococcus mutans ATCC 25175 was introduced into E. coli with xylitol-4-dehydrogenase (XDH) of Pantoea ananatis resulting in recombinant cells harboring the vector pETDuet-xdh-SmNox. The co-expression system exhibited optimal activity at a temperature of 37 °C and pH 8.5, and the addition of Mg2+ enhanced the catalytic activity by 1.19 fold. Co-expression of NADH oxidase with XDH enzyme resulted in increased L-xylulose concentration and productivity from xylitol as well as the intracellular NAD+ concentration. In a 1 L bioconversion system the final concentration and productivity of L-xylulose from 50 g/L of xylitol reached 48.45 g/L, and 2.42 g/L.h respectively. Overall, this study is a suitable approach for large-scale production of L-xylulose from xylitol.