Abstract: ObjectiveTo optimize expression conditions of ureB in Lactococcus lactis(L.lactis)engineering bacteria.MethodsNZ3900(pNZ8110/ureB)was constructed using recombinant DNA technology.With L₂₅(5⁶)orthogonal table design,inducer concentration,induction time point,and induction time were selected as the three factors,each one at five levels.After the nisin-induced expression,the quantities of ureB expressed in L.lactis with different combinations were compared to that determined with sodium dodecyl sulfate polyacrylamide gel electrophresis(SDS-PAGE).The ratio of target protein to total bacterial protein was analyzed with Genetools software after Gel scan.The primary and secondary relationships of factors and optimized conditions of protein expression were determined with mathematical statistics.The variance analyses of the results were performed with orthogonal variance analysis.ResultsThe maximum yield of ureB was 27.26 μg/mL of medium,and the maximum percentage of ureB in cell extracts of the L.lactis transformant was 20.19%.Resultsof variance analyses showed that the influence of inducing time on expression of ureB was statistically significant.ConclusionOptimized expression conditions of ureB in L.lactis engineering bacteria were determined.