IDENTIFICATION AND CHARACTERIZATION OF A MOBILIZING PLASMID, PND300, IN LACTOCOCCUS-LACTIS M189 AND ITS ENCODED NISIN RESISTANCE DETERMINANT

A 60 kb conjugative plasmid, pND300, which encodes nisin resistance, w as identified in Lactococcus lactis ssp. lactis (L. lactis) M189. pND3 00 was found to mobilize the transfer of some other plasmids as indica ted by the mobilization of plasmids encoding lactose utilization. The nisin resistance determinant from pND300 was initially subcloned on a 12 kb DNA fragment and subsequently reduced to 10.4 kb. Restriction an alysis, PCR, Southern hybridization and sequencing illustrated that th e nisin resistance of pND300 is very similar to that encoded by the tr ansposon involved in nisin production. pND300 encodes nisR as well as nisK and the recently reported nisF, nisE and nisG, but does not encod e nisI. The DNA fragment encoding the nis genes is flanked by IS946 wi th a copy at each end in reverse orientation. The expression of these nis genes is probably controlled by a putative promoter upstream of ni sR, which is composed of the TTGCAA hexanucleotide on the insertion se quence IS946 and the TATAAT sequence 21 bp downstream.