Production of L-xylulose from xylitol by a newly isolated strain of Bacillus pallidus Y25 and characterization of its relevant enzyme xylitol dehydrogenase

摘要

A novel facultative thermophilic bacterium capable of producing rare ketoses from polyols was isolated from soil and identified as Bacillus pallidus Y25.We have employed this isolated strain for the production of L-xylulose,a rare ketopentose,from xylitol by a resting cell reaction at 50 °C.After optimization of culture conditions and reaction states,L-xylulose was produced at up to 85% yield when 2% xylitol was utilized.The key enzyme responsible for the interconversion of xylitol and L-xylulose was purified to homogeneity and identified as NAD-dependent xylitol dehydrogenase(XDH-Y25),with a molecular mass of 28 kDa as determined by SDS-PAGE.XDH-Y25 is most active in glycine-NaOH buffer(pH 10)at 40 °C and its substrate specificity is restricted to D-threitol,xylitol and D-iditol.This suggested that the enzyme is specific for polyols that have a hydroxyl group at the C-2 and C-3 positions in the L-and D-sides,respectively,in the Fischer projection.N-terminal amino acid sequencing of XDH-Y25 revealed low homology to any known dehydrogenases.To our knowledge,this is the first report on the characterization of xylitol dehydrogenase from a Bacillus species.