In this study,in order to realize the simple and effective purification of levansucrase,the gene sacB from Bacillus amyloliquefaciens was added with histidine label and fused with the signal peptide gene usp45 to form the gene fragment usp45-sacB,then it was inserted into the plasmid pNZ8048 and introduced into L.lactis NZ9000 to construct the recombinant strain L.lactis(pNZ8048-usp45-sacB).It is verified by electrophoresis that the size of the purified protein is 51 kDa,which is in line with the expected size,and it is confirmed that the levansucrase is successful-ly expressed.In order to further improve the yield of levansucrase,the induction time and the concen-tration of inducer were optimized.The best expression conditions are as follows:the induction time is 48 h and the concentration of inducer nisin is 2 μg/L.
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