Antagonistic activity of Lactobacillus plantarum C11: two new two-peptide bacteriocins, plantaricins EF and JK, and the induction factor plantaricin A

Abstract

Six bacteriocinlike peptides (plantaricin A [PlnA], PlnE, PlnF, PlnJ, PlnK, and PlnN) produced by Lactobacillus plantarum C11 were detected by amino acid sequencing and mass spectrometry. Since purification to homogeneity was problematic, all six peptides were obtained by solid-phase peptide synthesis and were tested for bacteriocin activity. It was found that L. plantarum C11 produces two two-peptide bacteriocins (PlnEF and PlnJK); a strain-specific antagonistic activity was detected at nanomolar concentrations when PlnE and PlnF were combined and when PlnJ and PlnK were combined. Complementary peptides were at least 10(3) times more active when they were combined than when they were present individually, and optimal activity was obtained when the complementary peptides were present in approximately equal amounts. The interaction between complementary peptides was specific, since neither PlnE nor PlnF could complement PlnJ or PlnK, and none of these peptides could complement the peptides constituting the two-peptide bacteriocin lactococcin G. Interestingly, PlnA, which acts as an extracellular signal (pheromone) that triggers bacteriocin production, also possessed a strain-specific antagonistic activity. No bacteriocin activity could be detected for PlnN.

FIG. 1

Bacteriocinlike peptides encoded by pln genes. The peptides are characterized by their cationic character, their potential to form amphiphilic α-helices, and the fact that their genes encode precursors containing a typical double glycine leader peptide (7, 12). All of these peptides were detected in culture supernatants of L. plantarum C11 (see text for details).

FIG. 2

Helical wheel representations of PlnE, PlnF, PlnJ, and PlnK. The black and white boxes indicate polar and nonpolar residues, respectively. Glycine is included in both black and white boxes as it is treated as being neutral with respect to polarity.