Plantaricin JK

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.

Plantaricin EF and JK are both two-peptide bacteriocins produced by Lactobacillus plantarum C11. The mechanism of plantaricin EF and JK action was studied on L. plantarum 965 cells. Both plantaricins form pores in the membranes of target cells and dissipate the transmembrane electrical potential (Deltapsi) and pH gradient (DeltapH). The plantaricin EF pores efficiently conduct small monovalent cations, but conductivity for anions is low or absent. Plantaricin JK pores show high conductivity for specific anions but low conductivity for cations. These data indicate that L. plantarum C11 produces bacteriocins with complementary ion selectivity, thereby ensuring efficient killing of target bacteria.

Lactobacillus plantarum produces a number of antimicrobial peptides (bacteriocins) that mostly target closely related bacteria. Although bacteriocins are important for the ecology of these bacteria, very little is known about how the peptides target sensitive cells. In this work, a putative membrane protein receptor of the two-peptide bacteriocin plantaricin JK was identified by comparing Illumina sequence reads from plantaricin JK-resistant mutants to a crude assembly of the sensitive wild-type Weissella viridescens genome using the polymorphism discovery tool VAAL. Ten resistant mutants harbored altogether seven independent mutations in a gene encoding an APC superfamily protein with 12 transmembrane helices. The APC superfamily transporter thus is likely to serve as a target for plantaricin JK on sensitive cells.