Screening A Strain Of Production Of L-xylulose From Xylitol

L-xylulose is a ketopentose that is found to be a metabolite in various prokaryotic andeukaryotic metabolic pathways. This carbohydrate exists at very low concentrations in natureand therefore can be called a rare sugar. L-xylulose can strongly inhibit α-glycosidase, and ithas been used as a kind of hypoglycemic drug. L-xylulose can also be investigated as astarting material for the production of other significant rare sugars such as L-lyxose. Using aresting cell reaction, L-xylulose production from xylitol has been described in Pantoeaananatis, Alcaligenes and Bacillus pallidus. Due to the intricacies of L-xylulose production,in this study, many attempts were made in order to obtain a higher quantity and quality of thisrare sugar. The paper has been described here the isolation of the strain, with the capability ofproducing L-xylulose from xylitol by a resting cell reaction. The optimization of cultivationand reaction conditions was also studied.A bacteria ZN-14with efficient oxidization ability for the conversion of xylitol toL-xylulose was isolated and purified from soil samples, through the primary isolation andsecondary screening. We have employed this isolated strain for the production of L-xylulose,from xylitol by a resting cell reaction and the product was analyzed by HPLC and polarimeter.The strain was identified as Bacillus megaterium, based on the sequence analysis of16SrDNA and the general morphological and biochemical characteristics.The conditions of fermentation were optimized by single factor and statisticalexperimental design methods. By optimizing the conditions of Bacillus megaterium ZN-14,the optimum carbon source xylitol, nitrogen source yeast extract and peptone, minerals CaCl2,MgSO4, FeSO4and MnSO4, cultivating temperature37℃, liquid volume20mL/250mL andinitial pH6.8were obtained. The effects of the concentration of xylitol, yeast extract,peptone,CaCl2, MgSO4, FeSO4and MnSO4on L-xylulose production were investigated in shakingflasks using statistical experimental design methods. The optimum concentration of xylitol,yeast extract,peptone, CaCl2, MgSO4, FeSO4and MnSO4was35.58g/L,6g/L,6.41g/L,0.035g/L,0.36g/L,0.037g/L and0.036g/L respectively with the biomass being11.63g/Land xylitol dehydrogenase activity being2.47U/mL. Effects of substract concentration, pH value and reaction time on the L-xyluloseconversion were determined. The concentration of substrate was found to be optimal at20g/L.A higher conversion yield was obtained after about24hours. The resting cell is most active inin glycine-NaOH buffer (pH10). After optimization of culture conditions and reaction states,L-xylulose was produced at up to26.6%yield at a reasonable cost when2%xylitol wasutilized.