Bacteriocins are small peptides secreted by lactic acid bacteria to destroy competing microbes in their ecological niche.  These peptides are highly specific in their antagonistic spectrum.  Class IIa bacteriocins also target Listeria monocytogenes, a common food-born pathogen.  Piscicocins V1a and V1b are two class IIa bacteriocins secreted by Carnobacterium piscicola.  Although they are highly homologous, V1a is 100 times more lethal than V1b.  We are in the process of comparing the roles of the C-terminal domains of these peptides in their lytic activity.  Fluorescence spectroscopy has been used to monitor the binding of these peptides to mimetic membranes and infrared spectroscopy has been used to examine the structure of the molecules.  The activity of the peptides against Listeria and other strains of Carnobacteria will also be presented.  These studies will help in understanding structure:function relationships in bacteriocins for their future development as probiotics and food preservatives.