Characteristics and potential applications of circular bacteriocins

Bacteriocins are ribosomally synthesized peptides or proteins exerting anatagonistic activity toward organisms which are closely related to the producer strain. Circular bacteriocins are produced by Gram-positive bacteria, mainly lactic acid bacteria, and to a lesser extent by Bacillus , Clostridium and Staphylococcus genera. These bacteriocins are characterized by the head-to-tail cyclization of their backbone. The circular nature of these peptides makes them resistant to many proteolytic enzymes and provides great thermal and pH stability. Circular bacteriocins are divided into 2 subgroups based on their physicochemical properties and sequence identity. These bacteriocins are synthesized as linear precursors with a leader sequence which is cleaved off during maturation. The mature circular peptides are composed of 58–70 amino acid residues. Biosynthesis of circular bacteriocins requires three stages: cleavage of the leader sequence, circularization and export out of the cell. Circular bacteriocins have broad antimicrobial activity spectrum, including many food spoilage bacteria and pathogens, such as Listeria , Staphylococcus and Clostridum spp. Circular bacteriocins permeabilize the membrane of sensitive bacteria, causing loss of ions and dissipation of the membrane potential, and finally cell death. Enterocin AS-48 was the first identified circular bacteriocin and is best characterized so far. Circular bacteriocins or bacteriocin-producing lactic acid bacteria have great potential in food preservation, and possibly in pharmaceutical and cosmetic industries. Thanks to their properties, circular bacteriocins could be an alternative not only to preservatives and methods used to provide microbial food safety presently, but also to less stable, linear bacteriocins. 1. Characteristics and classification of circular bacteriocins. 2. Genetics of circular bacteriocins. 3. Biosynthesis of circular bacteriocins. 4. Structure of circular bacteriocins. 5. Modes of action of circular bacteriocins. 6. Enterocin AS-48. 7. Potential applications of circular bacteriocins. 8. Summary