Characteristics of Tn5307 exchange and intergeneric transfer of genes associated with nisin production

Transfer of the Lactococcus lactis 11454 nisin-sucrose conjugative transposon, Tn5307, was investigated to develop a methodology for conjugation of this element to other lactic acid bacteria. Tn5307 exchange was sensitive to temperature and pH but was not affected by protease or amylase treatments to donor cells. Moreover, conjugation studies demonstrated that the direct-plate method could be employed to rapidly identify LM2301 transconjugants able to transfer Tn5307 at least ten times more efficiently than 11454. Intergeneric transfer of nisin and sucrose genes between L. lactis and a dairy Enterococcus sp. was also investigated. Erythromycin-resistant Enterococcus sp. recipients were developed by electro-transformation with pGK13 or by conjugal introduction of the broad-host-range plasmid pAM beta 1. Matings between L. lactis 11454 and an Enterococcus sp. recipient that contained pAM beta 1 yielded sucrose-positive, nisin-immune transconjugants at a frequency of 2.3 x 10(-9) transconjugants per donor cfu. Agar-overlay assays for nisin production revealed that enterococcal transconjugants did not produce the bacteriocin, but DNA.DNA hybridization with a nisA-specific probe demonstrated that these bacteria had acquired the nisin structural gene.