BACTERIOCINS OF LEUCONOSTOCS ISOLATED FROM MEAT

Several bacteriocin-producing Leuconostoc strains have been isolated from meat and identified as Leuconostoc gelidum UAL 187, Leuconostoc paramesenteroides-La7a, Leuconostoc carnosum-Ta11a and Leuconostoc carnosum-La54a. All strains produce bacteriocins that are active against Listeria monocytogenes and other lactic acid bacteria of concern in meat spoilage. All of the bacteriocins studied are heat stable in acidic environments and are inactivated by a range of proteolytic enzymes but not by catalase or lysozyme. Most are detected early in the growth cycle and are produced at refrigeration temperatures and in a pH range of 4.0-7.0. Leucocin A-UAL187, produced by Leuconostoc gelidium UAL 187, is a small peptide (MW 3930) translated as a 61 amino acid prepeptide consisting of a 24 amino acid leader region and 37 amino acid active bacteriocin that is secreted. A probe designed from a region of the leucocin gene has been used to locate the bacteriocin genes in the other strains (La7a, La54a and Ta11a). Strong hybridization signals were detected from 8.9 MDa, 32 MDa and 8.9 MDa plasmids in strains La7a, La54a and Ta11a, respectively. The bacteriocin structural gene from Leuconostoc carnosum-Ta11a (leucocin B-Ta11a) has been cloned and sequenced and the bacteriocin shows 100% homology to leucocin A-UAL187; however, the prepeptide differs in six residues. The mature extracellular bacteriocin from strain UAL 187 was purified and characterized by precipitation, gel filtration, hydrophobic interaction chromatography followed by RP-HPLC and amino-terminal sequencing, whilst those of the other strains are in the process of being purified and characterized using similar techniques. Preliminary results indicate that they are all small peptides in the range of 3.5-4.0 kDa.