Characteristics of the plasmid pCS100 containing nisin resistant gene from Lactococcus lactis subsp lactis ATCC7962

Nisin-producing and nisin resistant L. lactis subsp. lactis ATCC7962 harbored six plasmids. To find a plasmid containing a nisin resistant gene, these plasmids were transformed into L. lactis LM 0230 of plasmid-free and nisin sensitive strain. After screening on nisin selection media containing nisin (150 μg/ml), several nisin resistant transformants were obtained and the level of nisin resistance was very similar to that of wild type L. lactis subsp. lactis ATCC7962. A 26.5 kb plasmid, named as pCS100, which confers resistance to nisin, was identified in transformants. The pCS100 was digested with EcoRI and Southern blot hybridization was done with nisI probe to localize the nisin resistant gene. A 4 kb EcoRI fragment showed a strong positive signal, and it was cloned into pBluescript for the potential selection marker.