Colm Scully, Jennifer Mahony, Juan Borrero, Paul D Cotter, Douwe van Sinderen, Philip Kelleher, Eoin Kelly, Paula M O'Connor
Bacteriocins from lactic acid bacteria (LAB) are of increasing interest in recent years due to their potential as natural preservatives against food and beverage spoilage microorganisms. In a screening study for LAB, we isolated a strain, Lactobacillus plantarum NI326, from olives with activity against a strain belonging to the beverage-spoilage bacterium Alicyclobacillus acidoterrestris spp. Genome sequencing of the strain enabled the identification of a gene cluster encoding a putative circular bacteriocin and proteins involved in its modification, transport and immunity. This novel bacteriocin, named plantaricyclin A (PlcA), was grouped into the circular bacteriocin subgroup II due to its high degree of similarity with other gassericin A-like bacteriocins. Purification of the supernatant of Lb. plantarum NI326 resulted in an active peptide with a molecular mass of 5,570 Da, corresponding to that predicted from the (processed) PlcA amino acid sequence. The Plc gene cluster was subsequently cloned and expressed in L. lactis NZ9000, resulting in the production of an active 5,570 Da bacteriocin in the supernatant. PlcA is produced as a 91-amino acid precursor with a 33 amino acid leader peptide. This leader peptide is predicted to be removed, after which the N- and C-termini are joined via a covalent linkage to form the mature 58 amino acid circular bacteriocin PlcA. This is the first report of a characterized circular bacteriocin produced by Lb. plantarum and the inhibition displayed against A. acidoterrestris sp1 highlights the potential use of this bacteriocin as a preservative in food and beverages.IMPORTANCE In this work we describe the purification and characterization of a new antimicrobial peptide, termed Plantaricyclin A (PlcA), produced by a Lactobacillus plantarum strain isolated from olives. This peptide has a circular structure, and all the genes involved in its production, circularization and secretion have been identified. PlcA shows antimicrobial activity against different strains, including Alicyclobacillus acidoterrestris, a common beverage spoilage bacteria causing important economic losses in the beverage industry every year. PlcA is the first circular antimicrobial peptide described from Lactobacillus plantarum.
