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Heterologous Expression of the Lactococcus lactis Bacteriocin, Nisin, in a Dairy Enterococcus Strain

Department of Food Science and Nutrition, University of Minnesota, St. Paul, Minnesota 55108

Received 2 November 2001/ Accepted 10 April 2002

The bacteriocin nisin is produced only by some strains of Lactococcus lactis, and to date production in other lactic acid bacteria has not been achieved. Enterococcus sp. strain N12ß is a nisin-immune transconjugant obtained from a nisin-producing donor (L. lactis ATCC 11454) and a dairy recipient (Enterococcus sp. strain S12ß), but it does not produce nisin. In this study, using PCR amplification, we confirmed that the whole nisin operon is likely present in Enterococcus sp. strain N12ß. Northern hybridization of total RNA from strain N12ß with a nisA probe and the results of reverse transcriptase PCR showed the lack of nisA transcription in this strain. However, nisA transcription was partially restored in strain N12ß upon growth in the presence of exogenous nisin, and the nisA transcription signal was intensified after an increase in the external nisin level. Furthermore, bioassays showed that active nisin was produced in a dose-dependent fashion by strain N12ß following induction by exogenous nisin. These results indicated that expression of the nisin genes in Enterococcus sp. strain N12ß depended on autoinduction via signal transduction. However, the amount of external inducing signal required was significantly greater than the amount needed for autoinduction in L. lactis.

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