CONTROLLED GENE-EXPRESSION SYSTEMS FOR LACTIC-ACID BACTERIA - TRANSFERABLE NISIN-INDUCIBLE EXPRESSION CASSETTES FOR LACTOCOCCUS, LEUCONOSTOC, AND LACTOBACILLUS SPP

A transferable dual-plasmid inducible gene expression system for use i n lactic acid bacteria that is based on the autoregulatory properties of the antimicrobial peptide nisin produced by Lactococcus lactis was developed. Introduction of the two plasmids allowed nisin-inducible ge ne expression in Lactococcus lactis MG1363, Leuconostoc lactis NZ6091, and Lactobacillus helveticus CNRZ32. Typically, the beta-glucuronidas e activity (used as a reporter in this study) remained below the detec tion limits under noninducing conditions and could be raised to high l evels, by addition of subinhibitory amounts of nisin to the growth med ium, while exhibiting a linear dose-response relationship. These resul ts demonstrate that the nisin-inducible system can be functionally imp lemented in lactic acid bacteria other than Lactococcus lactis.