Isolation of a Nisin-Producing Lactococcus lactis Strain from Kimchi and Characterization of its nisZ Gene

Bacteriocin-producing lactic acid bacteria were isolated from kimchi. One isolate producing the most efficient bacteriocin was identified and named Lactococcus lactis B2, based on the biochemical properties and 16S rDNA sequences. The B2 bacteriocin inhibited many different Gram positive bacteria including Lactococcus, Lactobacillus, Leuconostoc, Enterococcus, Streptococcus, and Staphylococcus, but did not inhibit Gram-negative bacteria. The bacteriocin was maximally produced at temperatures between $25^{\circ}C\;and\;30^{\circ}C$ and at the initial pH of 7.0. Ninety $\%$ of the activity remained after 10 min of heat treatment at $121^{\circ}C,\;and\;100\%$, after 1 h exposure to organic solvents. The bacteriocin was purified from culture supernatant by ammonium sulfate precipitation, CM Sepharose column chromatography, ultrafiltration, and finally, by reverse-phase HPLC. A 1.58-kb fragment was amplified from B2 chromosome by using a primer set designed from the published nisA sequence. Sequencing result showed that the fragment contained the whole nisZ and 5' portion of nisB, whose gene product was involved in postmodification of nisin. The upstream sequence, however, was completely different from those of reported nisin genes.