-Thirteen dairy propionibacteria were screened for catalase-insensitive, protease-sensitive inhibition of various Gram-positive and Gram-negative bacteria. Production of bacteriocin-like agents was identified in 8 ofthese cultures. The bacteriocin produced by Propionibacteriumjensenii B 1264 inhibited closely related propionibacteria and lactic acid bacteria and was bactericidal to Lactobacillus delbrueckii subsp. lactis ATCC 4797. It was produced in sodium lactate broth cultures during stationary phase; maximum activity was detected after 10 d of growth but only after IO-fold concentration of culture supematants. The bacteriocin was precipated by ammonium sulphate at 70 % saturation. The ammonium sulphate-concentrated, dialyzed bacteriocin was stable to 0.1-1.0 rnol-Lr' NaCI, 0.1-2.0 % SOS, 4 mol-L:' urea, 100 "C (60 min), pH 2-10 and organic sol vents (methanol, ethanol and isopropanol at 0-50 %). Batch anion exchange chromatography (pH 6.5) of the bacteriocin yielded 101 % activity and 15-fold increased purity. Flat bed analytical isoelectric focussing showed that the isoelectric point was between pH 3 and 3.5. SOS-PAGE yielded an estimated molecular mass between 6 and 9 kOa. The evidence suggests that this anionic bacteriocin is unique. © Inra/Eisevier, Paris.