Sixty-four lactococcal strains isolated from natural whey starters were screened for the presence of the nisin structural gene by polymerase chain reaction. Seven of them showed a specific PCR product of 320 bp; only two produced antagonistic activity and were resistant to nisin. Southern blots of SmaI-digested DNA from PCR-positive strains hybridized with a nisA probe displayed a location of the gene on different SmaI fragments. Among PCR-positive strains, nisin producers showed specific transcript after reverse transcriptase-PCR, as well as some non-nisin-producing strains. The RT-PCR product could not be shown in one non-nisin-producing PCR-positive strain.
Moschetti, G., Villani, F., Blaiotta, G., Baldinelli, A., & Coppola, S. (1996). Presence of non-functional nisin genes in Lactococcus lactis subsp. lactis isolated from natural starters. FEMS Microbiology Letters, 145(1), 27–32. https://doi.org/10.1016/0378-1097(96)00380-1