PURIFICATION AND AMINO-ACID-SEQUENCES OF PISCICOCINS V1A AND V1B, 2 CLASS IIA BACTERIOCINS SECRETED BY CARNOBACTERIUM-PISCICOLA V1 THAT DISPLAY SIGNIFICANTLY DIFFERENT LEVELS OF SPECIFIC INHIBITORY ACTIVITY

Two bacteriocins produced by Carnobacterium piscicola V1 were purified and characterized. Piscicocin V1a (molecular mass = 4,416 Da) and pis cicocin V1b (molecular mass = 4,526 Da) are nonlantibiotic, small, hea t-stable antibacterial peptides. Piscicocin V1b is identical to carnob acteriocin BM1, while piscicocin V1a is a new bacteriocin. Its complet e sequence of 44 amino acid residues has been determined. Piscicocin V 1a belongs to the class IIa bacteriocins having the consensus YGNGV mo tif. These peptides inhibit various gram-positive bacteria, including Listeria monocytogenes. Piscicocin V1a is approximately 100 times more active than piscicocin V1b against indicator strains. However, the an tagonistic spectrum is the same for both piscicocins. Comparison of th ese results with the analysis of the amino acid sequence and secondary structure predictions suggests that (i) the conserved N-terminal cons erved domain is involved in the receptor recognition and therefore in an ''all-or-none'' response against target bacterial cells and (ii) th e C-terminal variable and hydrophobic domain determines membrane ancho ring and therefore the intensity of the antagonist response.