Heterologous expression of Class IIb bacteriocin Plantaricin JK in Lactococcus Lactis.

Plantaricin JK (PlnJK) is a Class IIb LAB bacteriocin that includes two peptides; i.e., PlnJ and PlnK, which can synergistically halt many types of gram-positive bacteria, including food spoilage organisms. Purification of these peptides from natural lactic acid bacteria is difficult therefore, their application remains limited. To overproduce this two-peptide bacteriocin, the food-grade nisin-controlled expression (NICE) system was firstly used to heterologous expression of PlnJK. We constructed recombinant plasmids pNZ8124-plnJ and pNZ8124-plnK, and expression of PlnJ and PlnK was achieved in Lactococcus lactis NZ9000. A combination technique of XAD-2 macroporous resin, strong cation column, and reversed-phase high performance liquid chromatography were used to obtain recombinant proteins. Their molecular mass was quantified by ESI-MS and the results were 2929.32 Da and 3502.89 Da, respectively. An antimicrobial activity assay indicated that PlnJK had significant antimicrobial activities toward strains of Staphylococcus and the two peptides acted synergistically. Fluorescence leakage analysis indicated that PlnJK induced the increase of membrane permeabilization, which resulted in intracellular ion leakage, electrolytes efflux and ultimately cell death.