Optimization Of The Conditions On Expression Of CESH In Rhizobium Strain BK-20and Production Of L(+)-tartaric Acid With Its Immobilized Cells

L (+)-tartaric acid is one of natural small organic acids, which can be abstracted from Tartarus that is a by-product in port wine industry. The market demand of this organic acid is increasing progressively year by year for its wide application in all kinds of different industries such as food, pharmaceutical, chemistry, textile, electroplating industry and et al. At present, a novel approach for L(+)-tartaric acid production using stereospecific cis-Epoxysuccinate hydrolase (CESH) from microorganism to convert cis-epoxysuccinate directly has become an inevitable development trend.In this study, the conditions on expression of CESH in a strain of Rhizobium strain BK-20preserved in our lab was been optimized.Through the optimization of the media components and the cultural conditions, comparative appropriate media components and cultural condition were gained:5g/L sodium tartrate,1g/L sugar,0.5g/L NH4Cl,1mL/L corn steep liquor,1g/L KH2PO4,0.5g/L MgSO4; initial pH8.0,10%of the volume of liquid media,1%of inoculum concentration,30℃as the optimal fermentation temperature, fermentation last24h,36h as the optimal inoculum age.At last, the highest enzyme activity of the cells can reach3498.0±142.6U/g, the average enzyme activity was increased by643.31%compared with the previous cell unoptimized.On this basis, the conditions of cell immobilization were tested. Sodium alginate as the optimal embedding medium,0.1g/mL of cell concentration as the optimum, and1.5%of the gel concentration as the optimum were confirmed. The highest enzyme activity of the immobilized cells was as high as2817.2±226.7U/g. And what’s more, the immobilized cells show excellent operational and preservable stability, because they can be used successively in10times without loss their normal structure and high enzyme activity, even when immersed in physiological saline60days later.