Screening And Condition Optimization Of A D-psicose-producing Stain

The rare sugar which contain only small amounts in nature are kind of monosaccharides or their derivatives.D-psicose is a kind of rare sugar.In recent years,With the understanding of its value,people has began to pay close attention to D-psicose.In this paper,the D-psicose-producing strain sp.3G-17 was screened from soil by plate screen?paper chromatography and HPLC analysis.The strain was finally identified as Sinorhizobium based on the morphology and sequence of 16S rDNA analysis.Through single factor experiment and response surface optimization,we got the optimal medium which are:peptone 1%,yeast extract 0.5%,NaCl 1%,MgSO4·7H2O 0.05%,KH2PO4 0.28%,fructose 1%.And the best conditions of fermentation are temperature 32?,rotate speed 180r/min,initial pH 6.6,shake flask volume 35mL/250mL,cultivation time 60h.Under these conditions,enzyme activity of sp.3G-17 reaches 824.8U/L.The crude enzyme solution is purified by ammonium sulfate fractionation,dialysis and ion exchange chromatography.The recovery rate is 22.9%and the purification fold is 12.7.The study of enzymatic characterization shows that the optimal pH is 9.0,stability pH range from 7.0 to 10.0.The optimal temperature is 60?,the activity has good stability below 50 ?.The.metal ions had a great influence of on enzyme activity.Ca2+ and Fe2+ have stimulative effect,Na+?Co2+and K+ have partially inhibited effect,Cu2+ and Zn2+ have strong inhibited effect.The EDTA experiment shows that the enzyme may be a metal ion binding protein.