Gassericin A: a circular bacteriocin produced by lactic acid bacteria Lactobacillus gasseri

During the recent years extensive efforts have been made to find out bacteriocins from lactic acid bacteria (LAB) active against various food spoilage and pathogenic bacteria, and superior stabilities against heat treatments and pH variations. Bacteriocins isolated from LAB have been grouped into four classes. Circular bacteriocins which were earlier grouped among the four groups of bacteriocins, have recently been proposed to be classified into a different class, making it class V bacteriocins. Circular bacteriocins are special molecules, whose precursors must be post translationally modified to join the N to C termini with a head-to-tail peptide bond. Cyclization appears to make them less susceptible to proteolytic cleavage, high temperature and pH, and, therefore, provides enhanced stability as compared to linear bacteriocins. The advantages of circularization are also reflected by the fact that a significant number of macrocyclic natural products have found pharmaceutical applications. Circular bacteriocins were unknown two decades ago, and even to date, only a few circular bacteriocins from a diverse group of Gram positive organisms have been reported. The first example of a circular bacteriocin was enterocin AS-48, produced by Enterococcus faecalis AS-48. Gassereccin A, produced by Lactobacillus gasseri LA39, Reutericin 6 produced by Lactobacillus reuteri LA6 and Circularin A, produced by Clostridium beijerinickii ATCC 25,752, are further examples of this group of antimicrobial peptides. In the present scenario, Gassericin A can be an important tool in the food preservation owing to its properties of high pH and temperature tolerance and the fact that it is produced by LAB L. gasseri, whose many strains are proven probiotic.