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Strain C19, isolated from fermented cucumbers and identified as Lactobacillus plantarum, produced a bacteriocin. This bacteriocin, named plantaricin C19, was stable at acidic pH, was relatively thermostable, and had a molecular mass of about 3.5 kDa. It inhibited some pathogenic (i.e., Listeria spp.) and spoilage Gram-positive bacteria but had weak or no action against lactic acid bacteria. Its adsorption on sensitive and resistant bacteria was pH dependent and was reduced by pretreatment of cells with lipase or lysozyme. Curing treatments with acriflavine or novobiocin yielded nonproducing mutants sensitive to plantaricin C19.Key words: lactic acid bacteria, Lactobacillus plantarum, bacteriocin, protein.

Plantaricin SA6, a bacteriocin produced by Lactobacillus plantarum SA6, exhibited an inhibitory action against several mesophilic lactobacilli. It was stable at 90-100 degrees C at pH 2-4 and it remained stable in the presence of several organic solvents, urea or beta-mercaptoethanol. Plantaricin SA6 bound specifically to the cell surface of only plantaricin SA6-sensitive bacteria. The putative receptors are not destroyed by different hydrolytic enzymes added to the phosphate buffer. Plantaricin SA6 acted as a bactericidal agent lysing sensitive strains, that became more permeable to ortho-nitro-phenol-beta-galactoside and lost their intracellular K+ ions and u.v.-absorbing materials. Both the adsorption and lethal action of plantaricin SA6 were maximal between pH 4 and 7, but the range of temperature tested (5-37 degrees C) had no effect. Ions (of several salts such as MgCl2) inhibited the binding of plantaricin SA6 and protected cells against bacteriocin action.