[Cloning of Nisin resistent gene nisI from Lactococcus lactis and its application as a food grade selection marker].

To construct an E. coli-L. lactis shuttle expression vector with nisI as a food grade selection marker.According to the sequence of Nisin resistant gene nisI reported by GenBank, the nisI fragment was amplified by polymerase chain reaction with pLEB590 as template. After being sequenced, the amplicon was confirmed by Blast from NCBI. Then, the nisI was subcloned into the E. coli-L. lactis shuttle vector pMG36e, resulting in the plasmid pMG36e-NisI. The recombinant strain MG1363/pMG36e-NisI was obtained when the plasmid pMG36e-NisI was transformed into L. lactis MG1363 competent cell by electroporation.When the medium contained 20 IU Nisin/mL, the recombinant strain carrying pMG36e-NisI showed the same growth curve and genetic stability as L. lactis MG1363.The nisI gene could be used as a selection marker for construction of a food grade expression vector.